1. Variables and Expressions
Lesson 2-2

2. Vocabulary
A numerical expression is a mathematical phrase with only numbers and operation symbols (+, -, x, ÷).
Example:
An algebraic expression is a mathematical phrase that contains a variable and operation symbols.
A variable is a symbol (usually a letter) that stands for a number.
Algebraic expression: 5y + 2

3. Evaluating Numerical Expressions
Use PEMDAS (order of operations).
84 – 10 ÷ 2
84 – 5 79

4. Evaluating Algebraic Expressions
Replace the variable with the value that you are given.
Now we have a numerical expression.
Solve using order of operations.

5. Example: Evaluate 2b-8 for b=11
2(11)-8
Substitute the 11 for the variable.
22 - 8
Multiplying comes before subtracting. 14

6. Example 2: Evaluate 5x-y for x=12 and y=14
5(12) - 14 46

7. Homework Time