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Variables and Expressions
Lesson 2-2
Vocabulary
A numerical expression is a mathematical phrase with only
numbers and operation symbols (+, -, x, ÷).
Example: 8 + 5 - 2
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
Evaluating Numerical
Expressions

Use PEMDAS (order of operations).
84 – 10 ÷ 2
84 – 5
79
Evaluating Algebraic
Expressions



Replace the variable with the value that
you are given.
Now we have a numerical expression.
Solve using order of operations.
Example: Evaluate 2b-8 for
b=11
2b-8
2(11)-8
22 - 8
14
Substitute the 11 for
the variable.
Multiplying comes
before subtracting.
Example 2: Evaluate 5x-y for
x=12 and y=14
5x-y
5(12) - 14
60 - 14
46