Writing Expressions - 5th Grade

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Questions and Answers

What is the result of evaluating the expression $3x + 5$ when $x = 4$?

  • 15
  • 17 (correct)
  • 14
  • 12

When comparing the expressions $5x + 2$ and $3x + 8$, what value of $x$ would indicate $5x + 2$ is greater?

  • 3 (correct)
  • 1
  • 2
  • 4

What does the expression $2(x + 5)$ equal when $x = 3$?

  • 10
  • 14
  • 12
  • 16 (correct)

The expression $4x - 6$ is equal to what when $x = 2$?

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

Which of the following keywords indicates subtraction when translating a word problem?

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

What is the first step in evaluating the expression $x^2 + 2$ for $x = 3$?

<p>9 (A)</p> Signup and view all the answers

In the expression $x + 7$ compared to $2x + 3$, what condition must be met for $x + 7$ to be greater?

<p>4 (A)</p> Signup and view all the answers

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Study Notes

Writing Expressions - 5th Grade Study Notes

Evaluating Expressions

  • Definition: Finding the value of an expression by substituting numbers for variables.
  • Steps to Evaluate:
    1. Identify the expression and the values of the variables.
    2. Substitute the values into the expression.
    3. Follow the order of operations (PEMDAS: Parentheses, Exponents, Multiplication and Division (from left to right), Addition and Subtraction (from left to right)).
  • Example: For the expression (3x + 5) with (x = 2):
    • Substitute: (3(2) + 5)
    • Calculate: (6 + 5 = 11)

Comparing Expressions

  • Definition: Determining which expression has a greater value or if they are equal.
  • Methods:
    1. Evaluate both expressions: Substitute the same values for any variables and compute the results.
    2. Analyze the structure: Look for similarities or differences in the expressions' terms.
  • Example: Compare (2x + 3) and (x + 7) for (x = 4):
    • Evaluate (2(4) + 3 = 8 + 3 = 11)
    • Evaluate (4 + 7 = 11)
    • Conclusion: (2x + 3 = x + 7)

Translating Word Problems

  • Definition: Converting a word problem into a mathematical expression or equation.
  • Common Keywords:
    • Addition: sum, more than, increased by
    • Subtraction: difference, less than, decreased by
    • Multiplication: product, times, of
    • Division: quotient, divided by, per
  • Steps to Translate:
    1. Read the problem carefully.
    2. Identify the quantities involved and the operations required.
    3. Write the corresponding expression or equation.
  • Example: "Twice a number decreased by 5":
    • Let the number be (x):
    • Expression: (2x - 5)

Evaluating Expressions

  • Finding the value of an expression by substituting in variables.
  • Steps to evaluate:
    • Identify the expression and variable values.
    • Substitute values into the expression.
    • Follow the order of operations (PEMDAS): Parentheses, Exponents, Multiplication/Division (left to right), Addition/Subtraction (left to right).
  • Example for (3x + 5) when (x = 2):
    • Substitute: (3(2) + 5)
    • Calculate: (6 + 5 = 11)

Comparing Expressions

  • Determining the greater value or equality of expressions.
  • Methods to compare:
    • Evaluate both expressions by substituting the same variable values.
    • Analyze the structure for similarities or differences in terms.
  • Example comparing (2x + 3) and (x + 7) when (x = 4):
    • Evaluate (2(4) + 3 = 11)
    • Evaluate (4 + 7 = 11)
    • Conclusion: (2x + 3 = x + 7)

Translating Word Problems

  • Converting word problems into mathematical expressions or equations.
  • Common keywords:
    • Addition: sum, more than, increased by.
    • Subtraction: difference, less than, decreased by.
    • Multiplication: product, times, of.
    • Division: quotient, divided by, per.
  • Steps to translate:
    • Read the problem carefully.
    • Identify the quantities and required operations.
    • Write the corresponding expression or equation.
  • Example: "Twice a number decreased by 5."
    • Let the number be (x).
    • Expression: (2x - 5)

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