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.
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.