1. Variables in Expressions 8 th Grade Arizona State Standard – Evaluate an expression containing variables by substituting rational numbers for the variables.

2. Objective I will be able to substitute a rational number for a variable in order to evaluate algebraic expressions.

3. Why is this important?

4. Important Vocabulary Variable – a letter that is used to represent one or more numbers. Ex: x, y, z, a, b, c, … Algebraic Expression – collection of numbers, variables, operations, and grouping.

5. Examples Algebraic Expression 5 n 4 x 2 2 a + bc Verbal Description 5 times n 4 times the square of x 2 times a, plus b times c

6. More Vocabulary Term – a part of an expression that is separated by addition signs. Example: 3 x + (-2), the terms are 3x and -2 Substituting – Replacing each variable in an algebraic expression by a number Value of the expression – the number obtained after simplify the expression.

7. Steps for evaluating an expression 1. Write the algebraic expression 2. Substitute values for the variable 3. Simplify the numerical expression.

8. Example Evaluate 2 n + 5 when n = 13 (Write original expression) 2 (13) + 5 (Substitute 13 for n) 26 + 5 (Follow the Order of Operations to simplify) 31

9. Example Evaluate: 3 x 2 – 11 x when x = 6 3 x 2 – 11 x Step 1 – Write original expression 3 (6) 2 – 11(6) Step 2 – Substitute 3 (36) – 11 ( 6) Step 3 – Follow Order of Operations 108 – 66 Step 4 – Simplify 42

10. Real Life Example A rover driving on the moons surface travels at a speed of 60 ft/min. How far will it travel in 90 min? Distance = Rate x Time Rate = 60 ft/min Time = 90 min d = rt d = (60) (90) Distance = 5,400 ft

11. PRACTICE Page 24 # 3 – 8 Page 24 #9 – 40 Extra Practice – Page 716