1. Evaluate the expression for the given value(s) of the variable(s).
Example 4
Evaluating Algebraic Expressions
Evaluate the expression for the given value(s) of the variable(s). 3x + 4, x = 7 a. – s = 2, b. p 4
10s 3
3p 2,
SOLUTION 3x + 4 = 3 a. ( ) 7
Substitute 7 for x. = 21 + 4
Multiply. = 25
Add.

2. Example 4 b. 10s 3 – 3p 2 = 10 ( ) 3 2 – 3 ( ) 2 4 = 10 ( ) 8 – 3 16 =
Evaluating Algebraic Expressions b.
10s 3 –
3p 2 = 10 (
) 3 2 – 3 (
) 2 4
Substitute 2 for s and 4 for p.
Evaluate powers. = 10 ( ) 8 – 3 16 = 80
Multiply. – 48 = 32
Subtract.

3. Example 5
Evaluating a Real-Life Expression
WATERFALL
A river carries a stone over a waterfall. The stone hits the water 5 seconds later. To find the height of the waterfall, use the expression 16t2, which gives the distance in feet that a dropped object falls in t seconds.
SOLUTION
16t 2 = 16 (
) 2 5
Substitute 5 for t.
Evaluate the power. 16 ( ) 25 = =
400
Multiply.

4. The waterfall is about 400 feet high.
Example 5
Evaluating a Real-Life Expression
ANSWER
The waterfall is about 400 feet high.

5. Evaluate the expression for the given value(s) of the variable(s).
Guided Practice
for Examples 4 and 5
Evaluate the expression for the given value(s) of the variable(s).
17. 4r + 6, r = 5
ANSWER 26
18. ( ), 5 – y 3 = 8
ANSWER 9
19. n2 +
q3, n = 1, q 2
ANSWER 9

6. Guided Practice 20. WHAT IF?
for Examples 4 and 5
20. WHAT IF?
In Example 5, suppose the stone hits the water after 2 seconds. Find the height of the waterfall.
ANSWER
64 ft