Graph Theory: Planar Graphs and Euler Circuits

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Questions and Answers

What is a planar graph?

  • A graph where edges can cross each other
  • A graph that can be drawn without edges crossing (correct)
  • A graph with no vertices
  • A graph that includes a Hamiltonian circuit

A graph is considered planar if at least one of its edges crosses another.

False (B)

What term is used to describe a graph whose edges and vertices come from a given graph that is not planar?

subgraph

If a graph can be redrawn without any __________ between edges, it is classified as a planar graph.

<p>crossing</p>
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Match the following terms with their definitions:

<p>Planar Graph = A graph without intersecting edges Hamiltonian Circuit = A route that visits each vertex exactly once and returns to the starting point Subgraph = A graph formed from a subset of a given graph's vertices and edges Redrawing = The process of altering the layout of a graph to improve clarity</p>
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Which of the following statements about the Utilities Graph is true?

<p>It contains a Hamiltonian circuit. (D)</p>
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Redrawing edges such that they do not cross is always possible for any graph.

<p>False (B)</p>
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What main problem arises when trying to create a planar drawing of the Utilities Graph?

<p>Edges cross each other.</p>
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Which of the following statements is true about an Euler circuit?

<p>It begins and ends at the same vertex and uses each edge exactly once. (B)</p>
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An Euler circuit can exist in a graph if at least one vertex has an odd degree.

<p>False (B)</p>
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What is the term used for the number of edges that meet at a vertex?

<p>degree</p>
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A circuit that uses every edge exactly once is called an ______ circuit.

<p>Euler</p>
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In order for a graph to be Eulerian, which condition must be satisfied?

<p>All vertices must have an even degree. (C)</p>
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The path A–B–C–E–H–G–E–B–D–A is an Euler circuit.

<p>False (B)</p>
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How can Euler prove that a graph cannot have an Euler circuit?

<p>By examining the number of edges meeting at each vertex.</p>
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What time will it be 8 hours after 9 o’clock on a 12-hour clock?

<p>5 o’clock (D)</p>
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What is the minimum number of colors required to color the graph represented by the fictional map according to the content?

<p>4 (A)</p>
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A graph can be colored using only two colors if it has a ring of five vertices.

<p>False (B)</p>
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If the time now is 10 o'clock, then 7 hours ago it was 3 o'clock.

<p>True (A)</p>
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What day of the week is 16 days after Monday?

<p>Wednesday</p>
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What is the term used to describe a graph that can be colored with four colors?

<p>4-colorable</p>
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If today is Friday, then 14 days from now will also be _____

<p>Friday</p>
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The four-color theorem states that every planar graph can be colored with ______ colors.

<p>four</p>
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Match the following terms related to graph coloring with their definitions:

<p>Planar graph = A graph that can be drawn on a plane without edges crossing Vertex = A point where two or more edges meet Edge = A line connecting two vertices Graph coloring = The assignment of colors to the vertices of a graph such that no two adjacent vertices share the same color</p>
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Match the day with its corresponding number in modular arithmetic:

<p>Friday = 0 Saturday = 1 Sunday = 2 Monday = 3 Tuesday = 4 Wednesday = 5 Thursday = 6</p>
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Is the congruence 29 ≡ 8 mod 3 true or false?

<p>True (A)</p>
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In the fictional map example, how is connectivity between neighboring countries represented in the graph?

<p>By edges (D)</p>
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According to the four-color theorem, it is possible for a planar graph to require more than four colors.

<p>False (B)</p>
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The remainder of 16 divided by 7 is 2.

<p>True (A)</p>
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What strategy can be used to color the graph vertices effectively?

<p>Start with one vertex, assign it a color, and then assign colors to adjacent vertices while minimizing the number of new colors used.</p>
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What was the day of the week on July 4, 2017?

<p>Tuesday</p>
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What day of the week is July 4, 2022?

<p>Monday (D)</p>
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The year 2020 is not a leap year.

<p>False (B)</p>
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What is the result of $61 \mod 12$?

<p>1</p>
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To find what time it was 57 hours ago from 5 o’clock, calculate $(5 - 57) \mod ______$.

<p>12</p>
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Match the operations with their results:

<p>(33 - 16) mod 6 = 5 (14 - 27) mod 5 = 2 (23 + 38) mod 12 = 1 (5 - 57) mod 12 = 8</p>
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What does the expression 1826 modulo 7 represent?

<p>The remainder when 1826 is divided by 7 (D)</p>
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In modular arithmetic, the result of an operation mod n is always less than n.

<p>True (A)</p>
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How many extra days are counted in a leap year?

<p>1</p>
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What is the result of the expression (15 * 23) mod 11?

<p>4 (B)</p>
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The check digit of an ISBN is calculated using a multiplication modulo system.

<p>False (B)</p>
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How many digits are there in a standard ISBN number?

<p>13</p>
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If an integer x is 5, then the expression (x - 57) mod 12 results in __.

<p>8</p>
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Match the following ISBN components with their descriptions:

<p>d1 = First digit of ISBN country code = Indicates the region or country of publication publisher number = Represents the publisher identifier check digit = Final digit that ensures the correctness of ISBN</p>
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What is the purpose of the check digit in an ISBN?

<p>To ensure accuracy in data entry (D)</p>
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Transposition errors are rarely caught by the ISBN coding system.

<p>False (B)</p>
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What happens when an incorrect ISBN is sent?

<p>The receiving clerk calculates the check digit to verify its correctness.</p>
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What does each dot in a graph typically represent in social network connections?

<p>A friend (D)</p>
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In a graph, all edges must begin and end at vertices.

<p>True (A)</p>
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Who is the student that has only one study group in common with others?

<p>Kayla</p>
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Amber is involved in __________ study groups.

<p>three</p>
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Match the following students with their number of study groups:

<p>Amber = 3 Kayla = 1 Laura = 2 Dan = 2</p>
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Which type of connection in a graph indicates that two elements share a common attribute?

<p>Edge (B)</p>
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Multiple edges can exist between the same two vertices.

<p>True (A)</p>
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How many study groups does Laura have in common with the others?

<p>two</p>
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What is the purpose of a check digit in ISBN and UPC codes?

<p>To ensure the number is valid and to help catch errors (C)</p>
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The Luhn algorithm is used to validate credit card numbers based on modular arithmetic.

<p>True (A)</p>
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What is the final sum required for the Luhn algorithm to determine a valid credit card number?

<p>0 mod 10</p>
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The check digit for the ISBN of 'The Equation that Couldn't Be Solved' is _____

<p>3</p>
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Match the following coding systems with their descriptions:

<p>ISBN = Used primarily for books UPC = Used for grocery items Credit Card = Uses the Luhn algorithm for validation Bar Code = Represents product information in a machine-readable format</p>
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Which of the following statements about UPC is NOT true?

<p>UPC codes are used only for books (B)</p>
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UPC codes and ISBNs use the same method to calculate their check digits.

<p>False (B)</p>
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What is the typical length of a credit card number?

<p>13 to 16 digits</p>
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Which statement about an Euler circuit is true?

<p>Every edge must be traversed exactly once. (C)</p>
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For a graph to be Eulerian, at least one vertex must have an odd degree.

<p>False (B)</p>
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How can one determine if a graph has an Euler circuit?

<p>Check that all vertices have an even degree.</p>
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A path that begins and ends at the same vertex is known as a ______.

<p>circuit</p>
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Which of the following is an example of an Euler circuit?

<p>B–D–F–G–H–E–C–B–A (C)</p>
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An Euler circuit can exist in a graph if it has at least one vertex of even degree.

<p>False (B)</p>
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What observation did Euler make regarding the degree of vertices for an Euler circuit to exist?

<p>Each vertex must have an even degree.</p>
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What is the result of calculating $15 mod 6$?

<p>1 (C)</p>
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If today is Thursday, then 6 days from now it will be Thursday.

<p>False (B)</p>
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How many hours ago was it if the current time is 2 o’clock and it was at 9 o’clock?

<p>5</p>
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The result of $8 + 5$ on a 12-hour clock is _____

<p>1</p>
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Match the days of the week with their corresponding numbers in modular arithmetic:

<p>Monday = 0 Tuesday = 1 Wednesday = 2 Thursday = 3 Friday = 4 Saturday = 5 Sunday = 6</p>
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What day of the week is represented by the number 2 in modular arithmetic?

<p>Wednesday (A)</p>
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The congruence statement $29  8$ mod 3 is true.

<p>True (A)</p>
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What will be the time 7 hours ago if it is currently 9 o'clock?

<p>2</p>
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What is the minimum number of colors required to color the fictional map described in the content?

<p>4 (B)</p>
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The graph representing the fictional map is always 3-colorable.

<p>False (B)</p>
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What technique is suggested for coloring the vertices of a graph efficiently?

<p>Start with one vertex, color it, and then color connected vertices one by one.</p>
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Match the following concepts with their descriptions:

<p>Four-color theorem = Every planar graph can be colored with four colors Planar graph = A graph that can be drawn without edges crossing Graph coloring = Assigning colors to vertices without adjacent vertices sharing a color Neighboring countries = Countries that share a common boundary</p>
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How is the connectivity between neighboring countries represented in the graph?

<p>With edges connecting the vertices (B)</p>
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A graph can be colored with only three colors if it has a ring of five vertices.

<p>False (B)</p>
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The vertices of the graph are colored to ensure that no two vertices connected by an edge share the same ______.

<p>color</p>
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What is the relationship described by Euler's formula for a planar graph?

<p>$v + f = e + 2$ (C)</p>
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In graph theory, the region surrounding a graph is called the infinite face.

<p>True (A)</p>
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How many faces are counted in a planar graph with seven edges and five vertices, according to Euler's formula?

<p>4</p>
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In graph theory, which of the following is NOT a practical application of graph coloring?

<p>Creating non-planar graphs (A)</p>
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What is the term used for a graph that can be drawn on a plane without edges overlapping?

<p>Planar Graph</p>
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According to the four-color theorem, a planar graph may require more than four colors for proper coloring.

<p>False (B)</p>
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What is the minimum number of colors required to color the graph represented by the fictional map?

<p>4 (B)</p>
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The four-color theorem guarantees that a planar graph can use only three colors.

<p>False (B)</p>
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How does the connectivity between neighboring countries get represented in a graph?

<p>By drawing edges between vertices corresponding to the countries.</p>
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The graph in the example requires a minimum of _____ colors for proper vertex coloring.

<p>four</p>
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What is the total weight of the Hamiltonian circuit A-D-B-F-C-E-A?

<p>36 (D)</p>
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The Hamiltonian circuit mentioned can only be traversed in one direction.

<p>False (B)</p>
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What is the primary purpose of using weights in a graph?

<p>To represent quantities such as distances or costs.</p>
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The cost of traveling between cities can be represented as the weight of the _____ in a graph.

<p>edge</p>
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Match the following cities with the corresponding edge weights in the context of travel costs:

<p>London = 160 Paris = 250 Madrid = 240 Rome = 200</p>
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Which algorithm is mentioned for finding a low-cost route visiting each city exactly once?

<p>Greedy Algorithm (A)</p>
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The edge-picking algorithm guarantees an optimal route in all cases.

<p>False (B)</p>
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What was the smallest weight edge traveled to from Paris in the example?

<p>Madrid</p>
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The route A–D–B–F–C–E–A completes a _____ circuit.

<p>Hamiltonian</p>
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What happens when marking edges during the algorithm?

<p>They may either complete a circuit or add a third edge to a vertex. (A)</p>
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What condition must be met for a graph to contain an Euler circuit?

<p>All vertices have even degree. (A)</p>
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An Euler path can exist in a graph with all vertices having even degrees.

<p>False (B)</p>
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In the context of the Euler paths, which two cities had to be the start and end points for the photographer's trip?

<p>Alameda and Dover</p>
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Euler paths traverse every edge in a graph exactly ______.

<p>once</p>
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Match the following terms related to Euler circuits and paths with their definitions:

<p>Euler Circuit = Starts and ends at the same vertex, uses every edge once. Euler Path = Uses every edge once, does not require returning to the start. Eulerian Graph = A graph where every vertex has an even degree. Odd Degree Vertex = A vertex with an odd number of connecting edges.</p>
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Which of the following represents a valid Euler circuit for the given graph?

<p>B–A–F–B–E–F–G–E–D–G–B–D–C–B (A)</p>
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There are multiple Euler circuits possible in an Eulerian graph.

<p>True (A)</p>
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In a complete graph with six vertices, what can be said about the circuits found by algorithms?

<p>They often outperform trial and error methods. (C)</p>
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The greedy algorithm selects the highest weight edge at each step.

<p>False (B)</p>
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What is the total weight of the Hamiltonian circuit found using the greedy algorithm starting at vertex A?

<p>42</p>
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The edge with the smallest weight in the example was __________.

<p>BD</p>
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Which edge was chosen from vertex E in the greedy algorithm example?

<p>CE (C)</p>
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Match the algorithms with their characteristics:

<p>Greedy Algorithm = Chooses the cheapest option at each step Edge-Picking Algorithm = Highlights edges based on weight Hamiltonian Circuit = Visits all vertices and returns to the start Complete Graph = A graph where every pair of vertices is connected</p>
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In the edge-picking algorithm, edges with the same weight can be represented together.

<p>True (A)</p>
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What is Euler's formula related to in the context of planar graphs?

<p>The relationship between edges, vertices, and faces (D)</p>
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What is a characteristic feature of a complete graph?

<p>Every pair of vertices is connected by an edge.</p>
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In a planar graph, the exterior region is considered as one of the faces.

<p>True (A)</p>
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What is the minimum number of colors required to color any planar graph according to the four-color theorem?

<p>four</p>
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What is the first edge selected when using the edge-picking algorithm in the weighted graph?

<p>BD with weight 2 (C)</p>
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In Euler's formula, if a graph has 5 vertices and 4 faces, then it must have ______ edges.

<p>7</p>
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Match the following terms with their definitions related to graph theory:

<p>Vertices = Points in the graph where edges meet Edges = Lines connecting vertices Faces = Regions divided by edges in a planar graph Planar graph = A graph that can be drawn on a plane without crossing edges</p>
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What does the connection between map coloring and graph theory allow for?

<p>Efficient scheduling and task assignments (B)</p>
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A graph that can be colored with only two colors can contain cycles of any length.

<p>False (B)</p>
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What happens when neighboring countries share a border in graph theory?

<p>An edge is created between the corresponding vertices.</p>
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The region surrounding the graph in a planar drawing is known as the ______ face.

<p>infinite</p>
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According to the nonplanar graph theorem, which of the following graphs cannot be contracted to K5?

<p>Complete graph on five vertices (K5) (B)</p>
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What is required for a graph to be classified as Eulerian?

<p>All vertices must have an even degree. (D)</p>
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An Euler path requires returning to the starting point.

<p>False (B)</p>
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Name a city with an odd degree in the road example provided.

<p>Alameda or Dover</p>
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A path that visits every vertex exactly once is called a ______ circuit.

<p>Hamiltonian</p>
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How many vertices with odd degrees must exist for an Euler path to be possible?

<p>Exactly two (A)</p>
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All Euler circuits must cover each edge of the graph exactly twice.

<p>False (B)</p>
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What must a photographer do to successfully traverse all roads exactly once in the city map?

<p>Start at one of the cities with an odd degree.</p>
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An example of an odd degree vertex in the road map is ______.

<p>Alameda or Dover</p>
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What is a complete graph?

<p>A connected graph where every possible edge is drawn between vertices (C)</p>
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A graph is considered connected if all vertices can be reached from any other vertex.

<p>True (A)</p>
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What is the chromatic number of a planar graph according to the four-color theorem?

<p>Four (C)</p>
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What do you call an edge that begins and ends at the same vertex?

<p>loop</p>
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A nonplanar graph always requires four or fewer colors to color it.

<p>False (B)</p>
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A graph without any edges is considered __________.

<p>not connected</p>
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What is the minimum number of colors needed to color a graph so that no two connected vertices have the same color?

<p>chromatic number</p>
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Which of the following best describes equivalent graphs?

<p>Graphs that represent the same connections between vertices but may differ in arrangement (D)</p>
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In scheduling meetings among clubs with shared members, the number of required time slots corresponds to the graph's __________ for proper coloring.

<p>chromatic number</p>
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What is the significance of the edges in a graph?

<p>Edges represent connections between vertices.</p>
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Match the graph type with its continuous coloring conditions:

<p>Planar Graph = Can be colored with four colors Nonplanar Graph = May need more than four colors Two-colorable Graph = Can be colored with two colors Circuit Graph = Contains even number of vertices</p>
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What is the configuration of edges, vertices, and faces in a planar graph that verifies Euler’s formula?

<p>5 vertices, 4 faces, 7 edges (B)</p>
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In a planar graph, the infinite face is not considered a face.

<p>False (B)</p>
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What is Euler's formula for a planar graph?

<p>v + f = e + 2</p>
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A planar graph can be drawn in such a way that no edges __________.

<p>cross</p>
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Match each term with its corresponding definition:

<p>Vertices = Points in the graph representing objects Edges = Lines connecting the vertices Faces = Regions bordered by edges in the graph Infinite Face = The region outside the graph</p>
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How many colors are needed to color a map of countries, ensuring no two neighbors share the same color, as indicated by the content?

<p>4 (C)</p>
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Graph coloring can be applied in various practical applications, including scheduling tasks.

<p>True (A)</p>
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When counting the faces in a planar graph, what additional face must always be included?

<p>the infinite face</p>
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In graph theory, an edge connects two __________.

<p>vertices</p>
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A country is represented by a vertex in graph theory if it __________.

<p>is placed anywhere within its own boundary (D)</p>
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The graph in Figure 5.23 is 4-colorable.

<p>False (B)</p>
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A map can be colored using the fewest colors possible with __________ where no two adjacent countries share the same color.

<p>vertices</p>
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Match the following graph-coloring terms with their descriptions:

<p>Vertex = A point representing a country in a graph Edge = A connection between two vertices Planar graph = A graph that can be drawn without edges crossing Graph coloring = Assigning colors to vertices so no two adjacent share the same color</p>
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Which is true about the four-color theorem?

<p>It guarantees that no planar graph will require more than four colors. (C)</p>
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To color a graph effectively, you can reuse colors when connecting non-adjacent vertices.

<p>True (A)</p>
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If a graph requires fewer colors than the maximum, it is referred to as being __________.

<p>colorable</p>
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Why will a particular vertex need a fourth color in the example provided?

<p>It is adjacent to a ring of five vertices. (C)</p>
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What is the remainder when the product (15 * 23) is divided by 11?

<p>4 (C)</p>
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The check digit of an ISBN is calculated using an addition modulo system.

<p>False (B)</p>
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If the current time is 5 o'clock, what time was it 57 hours ago?

<p>8 o'clock</p>
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The first three digits of an ISBN are always _____ or 979.

<p>978</p>
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Match the following components of an ISBN with their descriptions:

<p>d1 = First digit of the ISBN d13 = Check digit 978 = Prefix for standard books 9 digits = Identifies country, publisher, and title</p>
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Which of the following statements correctly describes the traveling salesman problem?

<p>It finds the shortest route to visit each city once and return to the starting point. (D)</p>
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The Hamiltonian circuit must visit each city exactly once.

<p>True (A)</p>
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What is the total distance travelled by the route Chicago–New York–Dallas–Philadelphia–Atlanta–Washington, D.C.–Chicago?

<p>5197</p>
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The two algorithms mentioned for finding a solution in complete graphs are the greedy algorithm and the __________ algorithm.

<p>edge-picking</p>
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Match the following routes with their total distances:

<p>Chicago–New York–Dallas–Philadelphia–Atlanta–Washington, D.C.–Chicago = 5197 miles Chicago–Philadelphia–Dallas–Washington, D.C.–Atlanta–New York–Chicago = 5154 miles Chicago–Washington, D.C.–Dallas–New York–Atlanta–Philadelphia–Chicago = 5239 miles</p>
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Which statement about complete graphs is true?

<p>Every possible edge is drawn between vertices. (D)</p>
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Finding the optimal Hamiltonian circuit in a weighted graph has a known shortcut.

<p>False (B)</p>
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What is the total distance for the route Chicago–Washington, D.C.–Dallas–New York–Atlanta–Philadelphia–Chicago?

<p>5239</p>
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In the context of the traveling salesman problem, a route that visits each city only once is termed a __________ circuit.

<p>Hamiltonian</p>
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Which of the following statements accurately describes a Hamiltonian circuit?

<p>It visits each vertex once and returns to the starting vertex. (B)</p>
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Dirac’s Theorem guarantees that a graph is Hamiltonian if every vertex has a degree of at least $n/2$.

<p>True (A)</p>
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What does a weighted graph associate with each edge?

<p>a weight</p>
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A sequence of flights that starts and ends at the same city without visiting any city twice is represented by a Hamiltonian __________.

<p>circuit</p>
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Match the following theorems or concepts with their correct descriptions:

<p>Hamiltonian Circuit = A path that visits all vertices exactly once, returning to the start. Weighted Graph = A graph in which edges have associated values. Dirac's Theorem = A theorem providing conditions for the existence of Hamiltonian circuits. Flight Graph = A graph representing flights between cities as vertices connected by edges.</p>
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What is the significance of the weights on the edges of a weighted graph?

<p>They symbolize distances or costs associated with the connections. (C)</p>
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A Hamiltonian circuit can exist in a graph with vertices of varying degree, as long as there is a sufficient number of edges.

<p>False (B)</p>
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What is 7 hours before 3 o'clock on a 12-hour clock?

<p>8 o'clock (A)</p>
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16 days from Friday will be Saturday.

<p>False (B)</p>
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What day of the week is 14 days after Wednesday?

<p>Wednesday</p>
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Using modular arithmetic, 29 ≡ 8 mod ______.

<p>3</p>
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Match the following operations with their results on a 12-hour clock:

<p>10 + 5 = 3 8 - 9 = 7 11 + 4 = 3 2 - 5 = 9</p>
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Modular arithmetic can be used to represent day-of-the-week calculations.

<p>True (A)</p>
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Calculate 15 - 8 mod 12.

<p>7</p>
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If today is Monday, then 9 days from now will be a ______.

<p>Wednesday</p>
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What is a key characteristic of a planar graph?

<p>No edges cross over each other. (B)</p>
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The Utilities Graph can be redrawn in a way that does not have any edge crossings.

<p>False (B)</p>
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What is the term for a graph that is derived from another graph using its edges and vertices?

<p>subgraph</p>
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If a graph can be redrawn with no edges crossing, it is classified as a ______ graph.

<p>planar</p>
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Match each graph property with its correct description:

<p>Planar Graph = A graph with no edges crossing Hamiltonian Graph = A graph containing a Hamiltonian circuit Subgraph = A graph formed from a portion of another graph Non-planar Graph = A graph requiring edge crossings in any configuration</p>
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Which of the following statements about a subgraph is true?

<p>A subgraph can have fewer vertices and edges than the original graph. (C)</p>
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An equivalent form of a non-planar graph can still be classified as non-planar if it has crossing edges.

<p>True (A)</p>
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List one strategy to determine if a graph is not planar.

<p>Finding a non-planar subgraph</p>
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A graph that has edges which connect opposite vertices but require crossing is considered ______.

<p>non-planar</p>
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Which property makes the Utilities Graph non-planar?

<p>It contains a Hamiltonian circuit. (A)</p>
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Flashcards

Closed Path or Circuit

A path that starts and ends at the same vertex.

Euler Circuit

A circuit that uses every edge exactly once and never uses the same edge twice.

Degree of a Vertex

The number of edges that meet at a vertex.

Eulerian Graph

A graph where all vertices have an even degree.

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Non-Eulerian Graph

A graph that does not have an Euler circuit.

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Open Path

A path that does not begin and end at the same vertex.

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Non-Eulerian Graph Theorem

A graph with at least one odd degree vertex.

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Trial and Error

A method used to find a circuit that uses every edge in a graph, often using trial and error.

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Planar Graph

A graph that can be drawn without any edges crossing each other.

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Planar Drawing

A drawing of a graph where no edges cross.

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Subgraph

A graph where all edges and vertices belong to the original graph.

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Hamiltonian Circuit

A circuit that visits every vertex exactly once.

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Subgraph Method

A strategy to prove a graph is not planar by finding a subgraph which is not planar.

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The Utilities Graph

A specific graph used as an example to show that it is not planar.

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Non-Planar Graph

A graph that cannot be drawn without edges crossing.

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Redrawing

The process of redrawing a graph to find a planar drawing or to prove non-planarity.

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Map Coloring Problem

A map can be represented as a graph where countries are vertices and shared borders are edges. Coloring the map is equivalent to coloring the vertices of the graph so that adjacent vertices (countries with shared borders) have different colors.

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Chromatic Number

The minimum number of colors needed to color a map (or its corresponding graph) without adjacent regions (vertices) having the same color.

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Four-Color Theorem

A theorem that states that any map can be colored with at most four colors, so that no two adjacent regions share the same color.

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Trial and Error Coloring

A method to color a graph by trying different color assignments and checking if there are any conflicts.

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3-Colorable Graph

When a graph can be colored using only three different colors.

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Modular Arithmetic

A set of remainders after dividing by a specific number.

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Arithmetic modulo n

Performing arithmetic operations (addition, subtraction, etc.) and then finding the remainder after dividing by a given number.

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Result of Modulo n

The result of an arithmetic operation modulo n will always be a whole number smaller than the modulus (n).

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Addition Modulo n

Adding two numbers and then finding the remainder after dividing by the modulus.

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Subtraction Modulo n

Subtracting two numbers and then finding the remainder after dividing by the modulus.

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Clock Arithmetic

A special case of modular arithmetic where the modulus is 12, representing the 12 hours on a clock.

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Days of the Week Arithmetic

A special case of modular arithmetic where the modulus is 7, representing the 7 days of the week.

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Calculating Times

Calculating the time difference by performing subtraction modulo 12.

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ISBN (International Standard Book Number)

A 13-digit number used to identify books, consisting of three groups of digits: country/region, publisher, and title, with a final check digit ensuring accuracy.

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ISBN Check Digit

The last digit of an ISBN, calculated using a modular formula to verify the accuracy of the preceding digits.

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Modulo n Operation

A mathematical operation that finds the remainder after dividing a number by another number (the modulus).

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Modulus (in Modular Arithmetic)

The number by which another number is divided in a modulo operation, giving a remainder.

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ISBN Check Digit Calculation

The process of determining the check digit for an ISBN, involving a specific modular formula applied to the other digits.

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Transposition Errors

Errors in data input that are caused by accidentally switching the order of characters, such as numbers in an ISBN.

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ISBN Check Digit Verification

The process of applying a modular formula to an ISBN to verify if the entered digits are correct.

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Modular Arithmetic in Error Detection

The use of modular arithmetic to maintain accuracy and reduce errors in data, as seen in the ISBN system.

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Modulo (mod)

In modular arithmetic, this refers to the remainder when a number is divided by another number. For example, 16 mod 7 is equal to 2 because when 16 is divided by 7, the remainder is 2.

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Congruence (≡)

In modular arithmetic, two numbers are congruent if they leave the same remainder after division by a given number (the modulus). For example, 11 and 1 are congruent modulo 5 because they both leave a remainder of 1.

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Day-of-the-Week Arithmetic

A method to represent day-of-the-week calculations as 7-hour cycles. The days of the week are assigned numbers 0-6, and the remainder after division by 7 indicates the day after a specific amount of days.

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Modular Notation (a ≡ b mod n)

The notation used to represent the remainder obtained by dividing a number by another number. It's written as 'a ≡ b mod n', meaning 'a' leaves the same remainder as 'b' when divided by 'n'.

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Reducing Modulo n

When a number is larger than the modulus, it can be reduced to a smaller equivalent number within the range of the modulus. This is done by finding the remainder after division by the modulus. e.g. 17 ≡ 2 mod 5, because 17 divided by 5 leaves a remainder of 2.

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Modular Operations

Using modular arithmetic, this means performing calculations like addition or subtraction, but with the results adjusted as per the modulus. For example, 5 + 8 = 1 mod 12, because the 12-hour clock cycles back to 1.

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Vertex

A point on a graph representing an object in the network.

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Edge

A line connecting two vertices on a graph, signifying a relationship or connection between the objects.

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Euler's Circuit Theorem

A graph has an Euler circuit if and only if every vertex has an even degree.

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Euler's Formula

A relationship between the number of vertices (v), faces (f), and edges (e) in a planar graph, expressed as v + f = e + 2.

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Face in a Planar Graph

A region in a planar drawing of a graph that is enclosed by edges. This includes the region outside the graph, called the infinite face.

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Modulus (n)

The number that determines the size of the repeating cycle in modular arithmetic. The remainder after dividing by the modulus is the result of the operation within the cycle.

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What is an ISBN?

A 13-digit number used to identify books. It's divided into three parts: country/region, publisher, and title. The last digit is a check digit used to ensure accuracy.

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What is an ISBN Check Digit?

The last digit of an ISBN. It's calculated using a modular formula to verify the accuracy of the preceding digits. Any errors in the ISBN can be detected using the check digit.

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What is Modular Arithmetic?

A systematic way of working with remainders after division. It's useful in various applications, like error detection and encoding.

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What is a UPC?

A 12-digit number used to identify products, particularly in grocery stores. Like ISBN, it includes a check digit to ensure accuracy.

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What is the Luhn Algorithm?

An algorithm used by credit card companies to verify if credit card numbers are valid. It uses modular arithmetic (mod 10) to detect errors and prevent fraud.

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What is Clock Arithmetic?

A method of representing and calculating times using modular arithmetic, where the modulus is 12 (representing the 12 hours on a clock).

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What is Day-of-the-Week Arithmetic?

A method of representing and calculating days of the week using modular arithmetic, where the modulus is 7 (representing the 7 days of the week).

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What is a Transposition Error?

A type of error in data input that occurs when two digits are accidentally switched. Modular arithmetic can help detect these errors in ISBN and credit card numbers.

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Euler Path

A path that uses every edge exactly once, but doesn't have to return to the starting point.

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What is a Complete Graph?

A complete graph is a graph where every pair of vertices has an edge connecting them.

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Greedy Algorithm

The greedy algorithm for finding a Hamiltonian circuit involves choosing the edge with the smallest weight at each step, regardless of future consequences. It focuses on short-term gains.

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Edge-Picking Algorithm

The edge-picking algorithm involves repeatedly selecting the edge with the smallest weight available, ignoring previously visited vertices during the first phase. This can lead to a circuit that visits all vertices.

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Weight of a Circuit

The weight of a circuit is the sum of the weights of all the edges in the circuit.

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Weighted Graph

A weighted graph is a graph where each edge has a number associated with it, representing its 'weight' or cost.

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Starting Vertex

The vertex that the path starts at is called the starting vertex.

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Finding the 'Cheapest' Circuit

The algorithm aims to find a Hamiltonian circuit with the smallest possible total weight.

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Algorithms Aren't Perfect

The algorithms are not guaranteed to find the absolute shortest circuit; they are heuristics that do a good job, but might not be optimal.

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Total Weight of a Hamiltonian Circuit

The total weight of a Hamiltonian circuit is determined by summing the weights of all the edges in the circuit.

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Travel Cost in Weighted Graphs

An application of weighted graphs where the weight of an edge represents the cost of traveling between two vertices (cities).

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Hamiltonian Circuit for Travel Cost

An application of weighted graphs where the total weight of a Hamiltonian circuit represents the total cost of traveling between multiple cities, visiting each city only once, and returning to the starting point.

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Flight Cost in Weighted Graphs

An application of weighted graphs where the weight of an edge represents the flying cost between two cities. Finding the cheapest possible Hamiltonian circuit will give the most economical flight route.

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Greedy Algorithm Circuit Weight

The total weight of the Hamiltonian circuit found using the greedy algorithm.

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Edge Picking Algorithm Circuit Weight

The total weight of the Hamiltonian circuit found using the edge-picking algorithm.

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Loop

A path that begins and ends at the same vertex.

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Connected Graph

A graph where any vertex can be reached from any other vertex by following edges.

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Complete Graph

A connected graph where every possible edge is drawn between vertices.

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Equivalent Graphs

Graphs that represent the same connections between vertices, even if they look different.

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Path in a Graph

A movement from one vertex to another by traversing edges.

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Circuit

A path that starts and ends at the same vertex.

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Weight of a Hamiltonian Circuit

The sum of the weights of all the edges in a Hamiltonian circuit.

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Traveling Salesperson Problem

A problem where a salesperson needs to visit a set of cities, visiting each city exactly once and returning to the starting city, trying to minimize the total travel distance.

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Clock Addition Symbol (⊕)

The symbol used to denote addition on a 12-hour clock.

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Clock Subtraction Symbol (⊖)

The symbol used to denote subtraction on a 12-hour clock.

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What is Modulo (mod)?

The remainder obtained when one number is divided by another number.

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Study Notes

Introduction to Graphs

  • Graph theory is a branch of mathematics that analyzes connections.
  • Graphs are diagrams with vertices (points) and edges (lines or curves) connecting vertices.
  • Vertices represent entities, and edges illustrate relationships between them.
  • Graphs are used to model various connections, such as friendships on social media, roads between cities, and the internet.

Example 1 - Constructing a Graph

  • A table shows which students study together.
  • "X" indicates two students study in the same group.
  • Vertices represent students.
  • Edges connect vertices if corresponding students study together.

Example 1 - Solution

  • A graph shows how students are connected.
  • The student who participates in the most study groups is identified through the number of connections to other students.
  • The student with one connection is identified as someone who forms only one study group.

Introduction to Graphs (continued)

  • A graph can include vertices without edges or multiple edges connecting the same vertices; and an edge that is connected to the vertex (a loop).
  • A connected graph means any vertex can reach any other vertex by following edges.
  • In a complete graph, every possible edge is drawn between all vertices.
  • Graphs can represent various relationships and connections in real-world scenarios.

Euler Circuits

  • Euler circuits are paths that use every edge exactly once in a graph.
  • Euler circuits are called Eulerian.
  • The graph must have all even degrees of vertices.
  • The Königsberg bridges problem is solved by representing the land regions as vertices and connecting two vertices if a bridge exists between them.
  • Euler circuits are important in solving problems involving traversing edges exactly once.

Euler Paths

  • Euler paths are paths that use every edge exactly once (without returning to the starting point).
  • The graph must have exactly two vertices of odd degree.
  • The Euler path must start at one odd degree vertex and end at the other point of odd degree vertex.
  • Euler paths are used for route planning and traversing networks.

Weighted Graphs

  • A weighted graph has edges with values (weights), which can represent any quantity (e.g., distance, cost).
  • For Hamiltonian circuits in a weighted graph, summing the weights along the traversed edges yields the total distance traveled.
  • The traveling salesman problem seeks the shortest total distance for a Hamiltonian circuit, where the goal is to travel to all locations and return to the starting point in the shortest possible way.
  • Weighted graphs are used to model problems with various quantities associated with relationships.

Hamiltonian Circuits

  • A Hamiltonian circuit is a path that visits every vertex exactly once and returns to the starting vertex.
  • Dirac's theorem gives conditions for a graph to contain a Hamiltonian circuit: the connected graph must have at least 3 vertices, and every vertex has a degree equal to or greater than n/2, where n is the number of vertices.
  • The greedy algorithm and edge-picking algorithm are strategies for finding good Hamiltonian circuits. These methods can find a solution that might not be the absolute best but one that is "pretty good" or a "good solution" based on the given constraints.
  • Hamiltonian circuits are vital in problems like finding optimal routes or tours through a network of locations.

Planarity

  • A planar graph can be drawn on a plane so that no edges intersect.
  • The utilities graph puzzle is illustrated with three utility companies and three houses; if the pipes connect without crossing, the graph is planar; if they cross, the graph is nonplanar.
  • A subgraph of a graph consists of vertices and edges from the graph.
  • K5 is a complete graph with five vertices.
  • The subgraph theorem states that if a graph contains a non-planar subgraph (like the Utilities Graph or K5), the graph itself is non-planar.
  • Contractions in graphs provide a way to investigate nonplanar graphs and identify if such a graph is a subgraph of a larger graph.
  • Planar graphs are crucial in many applications involving physical layouts, like map designs.

Euler's Formula

  • Euler's formula relates the number of vertices (v), edges (e), and faces (f) of a planar graph via the relationship v + f = e + 2.

Graph Coloring

  • Graph coloring is used to color each vertex of a graph such that no two connected vertices share the same color.
  • The chromatic number is the minimum number of colors required to color a graph so that each edge connects vertices of different colors.
  • The four-color theorem states that every planar graph is 4-colorable, so only 4 colors are required to complete such a coloring.
  • Applications of graph coloring are widely varied and include scheduling problems; colorings are done so that when vertices are connected, they are not the same colors.
  • Graph coloring is used in various scenarios where conflicts need to be avoided, and scheduling or design problems require careful assignment of different resources to avoid simultaneous use of the same resource.

Modular Arithmetic

  • Modular arithmetic works with remainders when integers are divided.
  • Modular arithmetic is used for clock arithmetic and day-of-the-week calculations; 'modulo n' refers to the repeated pattern of mathematical results based on the remainder after division.
  • The concept of modulus n provides a mathematical framework for phenomena that repeat in cycles or involve cyclic patterns in mathematics.

Mathematical Systems

  • Mathematical systems describe and model how a set of elements behaves with certain operations.
  • Modular arithmetic is a specific system with certain rules for addition and subtractions, resulting in predictable patterns that are fundamental to many aspects of applied mathematics.
  • Mathematical systems provide structure and models for various forms of data/information analysis, problem solving, and pattern recognition.

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