Discrete Mathematics Exam II

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Questions and Answers

What is the primary rule regarding resources allowed during the exam?

  • Students may use notes as references.
  • Calculators are encouraged for problem-solving.
  • The exam is closed-book and no outside resources are allowed. (correct)
  • Communication with peers is permissible.

How should a student handle a question they find difficult during the exam?

  • Skip it and move on without marking it.
  • Mark it and return to it later. (correct)
  • Attempt to solve it even if it takes a long time.
  • Spend the entire time focusing on that question.

What is the total number of scoring points available in the exam?

  • 90 points, with no possibility of extra credit.
  • 100 points, plus up to 10 points in extra credit. (correct)
  • 110 points, totaling both the main exam and extra credit.
  • 100 points, with an additional 5 points for extra credit.

How should students indicate they need extra space for their answers?

<p>Write 'continued' on the extra sheet. (C)</p> Signup and view all the answers

What should students be cautious about when reading the exam questions?

<p>New combinations or variations of questions could appear. (A)</p> Signup and view all the answers

What is the correct expression for the inductive step in proving P(n) by mathematical induction?

<p>∀k(P(k) =⇒ P(k + 1)) for all positive integers k (B)</p> Signup and view all the answers

If a task can be accomplished in either n1 ways or n2 ways, what is the total number of ways to complete the task?

<p>n1 + n2 by the sum rule (A)</p> Signup and view all the answers

How many different ways can a 5-letter password be chosen from 52 letters without repeating any letter?

<p>52!/47! (B)</p> Signup and view all the answers

How many one-to-one (injective) functions can be formed from a set A to itself if |A| = 5?

<p>5! (B)</p> Signup and view all the answers

How many bit strings of length 10 do not contain a consecutive sequence of 9 '1's?

<p>29 − 2 (A)</p> Signup and view all the answers

What is the number of ways to choose an unordered team of 40 students from 89 registered students?

<p>C(89, 40) (C)</p> Signup and view all the answers

In how many different ways can a committee of 3 members be formed from a group of 10 members?

<p>C(10, 3) (A)</p> Signup and view all the answers

What is the product rule in counting?

<p>It applies when there are multiple stages and options at each stage. (A)</p> Signup and view all the answers

What is the correct expression for S1 + S2?

<p>$\sum_{j=0}^{n} (2 \cdot 3^{j} + 3 \cdot 2^{j})$ (C)</p> Signup and view all the answers

Which type of progression does the sum of terms represent?

<p>Geometric progression (B)</p> Signup and view all the answers

If set A is countably infinite, which statement is true?

<p>All of the above (D)</p> Signup and view all the answers

What is the relationship between the cardinality of the sets Z and N?

<p>|Z| = |N|, and both are countably infinite (C)</p> Signup and view all the answers

What do the symbols in the expressions for S1 and S2 represent?

<p>A series of geometric terms (A)</p> Signup and view all the answers

How can one define the countable infinity of set A?

<p>It can be matched directly to the natural numbers (C)</p> Signup and view all the answers

What is the key difference between countably infinite and uncountably infinite sets?

<p>Countably infinite sets can be listed, whereas uncountably infinite cannot (A)</p> Signup and view all the answers

In the context of set theory, what can be inferred about the cardinality of the natural numbers N?

<p>It is always greater than the cardinality of any finite set (C)</p> Signup and view all the answers

Which formula correctly represents the sum of the first n positive integers?

<p>$n(n + 1)/2$ (A)</p> Signup and view all the answers

How many different arrangements can three people have when seated around a circular table?

<p>6 (B)</p> Signup and view all the answers

What is the sum of the geometric series $1 + 2 + 4 + ... + 2^n$ for any non-negative integer n?

<p>$2^{n+1} - 1$ (C)</p> Signup and view all the answers

What is a valid statement about the set of positive odd integers?

<p>It is countably infinite. (A)</p> Signup and view all the answers

What is the result of $1 + 2 + 2^2 + ... + 2^n$?

<p>$2^{n+1} - 1$ (D)</p> Signup and view all the answers

Which concept is essential for proving the sum of the first n positive integers using induction?

<p>Base case validation (C)</p> Signup and view all the answers

Which of the following formulas is used for the sum of a finite geometric series?

<p>$S_n = rac{ar^{n+1} - a}{r - 1}$ for r ̸= 1 (D)</p> Signup and view all the answers

How many bit strings of length 10 start with six 0s or end with five 0s?

<p>192 (D)</p> Signup and view all the answers

Flashcards

Discrete Mathematics Exam II

A math exam covering discrete mathematics concepts.

Closed-book exam

An exam where students are not allowed to use books, notes, or other materials during the exam.

Multiple choice questions

Questions with a set of possible answers, only one of which is correct.

Exam scoring

The exam is scored out of 100 points, potentially with additional extra credit.

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Time management

Distribute time effectively. Don't linger on a particular problem.

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Read all questions carefully

Examine questions for any new combinations or variations of previous homework problems.

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Exam II

The second exam in a discrete mathematics course.

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Date of Exam II

Thursday, 25 April, 2024

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S1 + S2 (part a)

The sum of two series, S1 and S2, where each term in S1 is a product of powers of 3 and 2. The sum of the series is given by ∑ (3+2)^j for j from 0 to n

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S1 + S2 (part b)

The sum of two series, S1 and S2, where the terms in each series are powers of 3 and 2. For any j, S1 term = 3^j and S2 term= 2^j, The sum of the series is ∑ (3j + 2j) for j from 0 to n.

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S1 + S2 (part c)

The sum of two series. S1 and S2, where the terms in S1 are the powers of 3 & S2 are powers of 2. In this case, The combined sum is ∑(3 * 2)^j, for j from 0 to n.

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Arithmetic Progression

A sequence of numbers such that the difference between consecutive terms is constant.

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Geometric Progression

A sequence of numbers such that the ratio between consecutive terms is constant.

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Countably Infinite Set

A set that can be put into a one-to-one correspondence with the natural numbers.

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Injection (A to N)

A function that maps each element of set A to a unique element in the set of natural numbers N, while some elements of N may not be used.

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Surjection (N to A)

A function that maps every element of the set of natural numbers N to some element in set A. Every element of A must be mapped to.

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Bijection

A function that is both injective and surjective, creating a one-to-one correspondence between two sets.

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|Z| vs |N| (Cardinality)

The cardinality of the set of integers (Z) is equal to the cardinality of the set of natural numbers (N).

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Sum of first n natural numbers formula

The sum of the first n natural numbers (1 + 2 + 3 + ... + n) is equal to n(n + 1)/2

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Sum of a finite geometric series formula

The sum of the first n+1 terms of a geometric series (a + ar + ar^2 + ... + ar^n) is equal to (ar^(n+1) - a)/(r - 1), given r ≠ 1.

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Sum of the first n powers of 2

The sum of 1 + 2 + 2^2 + ... + 2^n is equal to 2^(n+1) - 1

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Countably infinite set example

Positive odd integers (Zodd = {1, 3, 5,...}) are countably infinite, meaning they can be put in a one-to-one correspondence with the natural numbers.

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Circular seating arrangements

The number of ways to seat n people around a circular table, where two arrangements are the same if each person has the same neighbors is (n-1)!.

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Bit strings with specific prefixes/suffixes

The number of bit strings of length 10 that either begin with six 0s or end with five 0s or both is 2^4+2^5-2^3=16+32-8=40

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Mathematical Induction - Inductive Step

For all positive integers k, if P(k) is true, then P(k+1) is also true.

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Permutations (P(n,r))

The number of ways to arrange r items from a set of n items, where order matters and repetition is not allowed.

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Combinations (C(n,r))

The number of ways to choose r items from a set of n items, where order doesn't matter and repetition is not allowed.

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Sum Rule

If a task can be done in n1 ways or n2 ways (mutually exclusive), then there are n1+n2 total ways to do the task.

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Product Rule

If a task can be done in n1 ways and another task can be done in n2 ways, then both tasks can be done together in n1*n2 ways.

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One-to-one (Injective) Function

A function where each element in the domain maps to a unique element in the range. No two inputs map to the same output.

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Password Length Calculation

Choosing a password of length k from distinct items (no repetition), there are n * (n-1) * ... * (n - k + 1) possible ways. (n choose k, is a combination formula).

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Bit Strings - Consecutive 1's

Find the number of bit strings of a certain length with no consecutive 9 1's.

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Selecting a team of Students

The number of ways to choose an unordered team of 40 students from a class of 89 registered students

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Study Notes

Discrete Mathematics Exam II - Critical Information

  • Exam Type: Closed-book
  • Materials Allowed: No notes, internet, calculators, programs, or communication devices.
  • Work Style: Work efficiently. If a problem is difficult, move on and come back to it later.
  • Question Format: Read questions carefully. Expect variations and new combinations of previous homework questions.
  • Continued Work: Use the back of previous pages or blank pages for additional space. Indicate the continuation with "continued" or "cont" and the problem number.
  • Scoring: Exam is out of 100 points total, plus possible extra credit of 10 points.
  • Multiple Choice: Multiple choice questions have only one correct answer. Numbers may differ from other exams.

Discrete Mathematics Exam II - Exam Questions

  • Question 1 (6 pts.): Σ (3⁰ + 2⁰) for integers n > 0

    • Options (choose one): a) Σ (3⁰ + 2⁰) = (3+2)^n b) Σ (3⁰ + 2⁰) = Σ(3⁰) + Σ(2⁰) c) Σ (3⁰ + 2⁰) = (3 + 2) d) none of the above
  • Question 2 (6 pts.): Sum of terms (23^2 + 32^2)

    • Options (choose one): a) arithmetic progression b) geometric progression c) both a and b d) none of the above
  • Question 3 (6 pts.): If set A is countably infinite

    • Options (choose one): a) injection from A to set of natural numbers b) surjection from set of natural numbers to A c) bijection between A and set of natural numbers d) all of the above e) none of the above
  • Question 4 (6 pts.): Cardinality

    • Options (choose one): a) If Z is uncountably infinite and N is countably infinite, |Z| > |N| b) If Z and N are both uncountably infinite, |Z| > |N| c) If Z and N are countably infinite, |Z| = |N| d) none of the above
  • Question 5 (6 pts.): Mathematical Induction

    • Options (choose one): a) To prove P(n) by induction, prove k(P(k) => P(k+1)) b) P(1) => P(k) => P(k+1) => P(n) c) P(1) => for all k(P(k) => P(k+1)) => P(n) d) (P(1) ∧ (P(k) ∧ P(k+1)) => P(n))
  • Question 6 (6 pts.): Combining task possibilities. Given n₁ and n₂ task ways.

    • Options (choose one): a) n₁ + n₂ by sum rule b) n₁ * n₂ by product rule c) n₁! * n₂! by product rule d) None of the above
  • Question 7 (6 pts.): Determine the number of possible 5-letter passwords using the English alphabet (case-sensitive). No letters can be repeated.

  • Question 8 (6 pts.): Number of one-to-one functions from set A to itself, where |A| = 5.

  • Question 9 (6 pts.): Bit strings of length 10 with no consecutive nines.

  • Question 10 (6 pts.): Number of ways to choose an unordered team of 40 students from 89 students.

Discrete Mathematics Exam II - Induction Proof

  • Question 2.1: Prove by induction that 1+2+3+…+n = n(n+1)/2 for any integer n ≥ 1.
  • Question 2.2: Prove by induction that 1+2^1+2^2+……+2^n = 2^(n+1)-1 for any integer n is ≥ 0

Discrete Mathematics Exam II - Counting

  • Question 3.1: Is the set of positive odd integers countably infinite? Provide a function proof.
  • Question 3.2: How many ways are there to seat three people around a circular table with three chairs?
  • Question 3.3: How many bit strings of length 10 either begin with six 0s or end with five 0s (or both)?

Discrete Mathematics Exam II - Extra Credit

  • Question 4: Prove the formula for the sum of a finite geometric progression. Use mathematical induction.

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