Page 485 - Basic College Mathematics with Early Integers

462 C HAPTE R 6 I PERCENT

Concept Check Consider the question:“78 is what percent of 350?”
Which part of the percent proportion is unknown?
a. the amount b. the base c. the percent
Now consider the statement:“14 is 10% of some number.”
Which part of the percent proportion is unknown?
a. the amount b. the base c. the percent

PRACTICE 8 Example 8 Solving Percent Proportion for the Base
75% of what number is 60?
150% of what number is 30?
t

T T T
Solution: percent base amount

30 150
= Write the proportion.
b 100

30 = 3 Write 150 as .
3
b 2 100 2

#
#
30 2 = b 3 Set cross products equal.
#
60 = b 3 Multiply.
60 Divide 60 by 3, the number multiplied by b.
= b
3
20 = b Simplify.
Thus, 150% of 20 is 30.
Work Practice 8

Concept Check When solving a percent problem by using a proportion,
describe how you can check the result.

PRACTICE 9 Example 9 Solving Percent Proportion for the Base
15.2 is 5% of what number?
20.8 is 40% of what number?
t

T T T
Solution: amount percent base
20.8 40 20.8 2 40
= or = Write the proportion and simplify .
b 100 b 5 100
#
#
20.8 5 = b 2 Set cross products equal.
#
104 = b 2 Multiply.
104
Answers = b Divide 104 by 2, the number multiplied by b.
2
8. 80 9. 304
52 = b Simplify.
Concept Check Answers Copyright 2012 Pearson Education, Inc.
So, 20.8 is 40% of 52.
c, b
By putting the result into the Work Practice 9
proportion and checking that the
proportion is true