Evaluate variable expressions involving integers
In algebra, letters (like x) stand in for numbers. 'Evaluating an expression' means you get to be the code-breaker! You are given the secret value of the letter, and your job is to plug it in and solve the problem.
Do this: Read the concept below, then try the quiz or activity.
Concept
A variable expression is a math phrase that contains numbers, operations (+, -, x, ÷), and at least one variable (a letter, like x or y). To evaluate it, you replace the variable with its given value and then perform the operations.
The Three-Step Process:
1. Substitute: Replace the variable with the number it stands for. It's a good idea to use parentheses when you substitute to keep things clear. 2. Simplify: Perform the calculations using the order of operations (PEMDAS). 3. Solve: Find the final value of the expression.
Example 1: Evaluate 5x - 3 when x = 4.
1. Substitute: Replace 'x' with 4.
* 5(4) - 3
2. Simplify: Remember that 5x means 5 *times* x.
* 5 x 4 = 20
* Now the expression is 20 - 3.
3. Solve:
* 20 - 3 = 17.Example 2: Evaluate y/3 + 2 when y = -12.
1. Substitute: Replace 'y' with -12.
* -12/3 + 2
2. Simplify: Division comes before addition (PEMDAS).
* -12 ÷ 3 = -4
* Now the expression is -4 + 2.
3. Solve:
* -4 + 2 = -2.Try it
Practice: Evaluate variable expressions involving integers.