Basic Mathematics for College Students

1

502 Chapter 6 Percent

SolutionWe begin with nitrogen.

Drop the % symbol and write 78 over 100.

Nitrogen makes up 10078 , or , of Earth’s atmosphere. 3950



39

50

To simplify the fraction, factor 78 as 2 39 and 100 as 2 50. Then

 remove the common factor of 2 from the numerator and denominator.

2

1

 39

2

1

 50

78%

78

100

Oxygen makes up 21%, or 10021 , of Earth’s atmosphere. Other gases make up

1%, or 1001 , of the atmosphere.

EXAMPLE (^3) Unions In 2007, 12.1% of the U.S. labor force belonged to
a union. Write this percent as a fraction in simplest form. (Source:Bureau of Labor
Statistics)
StrategyWe will drop the % symbol and write the given number over 100. Then
we will multiply the resulting fraction by a form of 1 and simplify, if possible.
WHYWhen writing a percent as a fraction, the numerator and denominator of the
fraction should be whole numbers that have no common factors (other than 1).
Solution
Drop the % symbol and write 12.1 over 100.
To write this as an equivalent fraction of whole numbers,we need to move the
decimal point in the numerator one place to the right. (Recall that to find the product
of a decimal and 10, we simply move the decimal point one place to the right.)
Therefore, it follows that is the form of 1 that we should use to build.
Multiply the fraction by a form of 1.
Thus,. This means that 121 out of every 1,000 workers in the U.S.
labor force belonged to a union in 2007.

12.1%1,000^121

Since 121 and 1,000 do not have any common factors

 (other than 1), the fraction is in simplest form.

121

1,000

Multiply the numerators.

 Multiply the denominators.

12.1 10

100  10

12.1

100



12.1

100



10

10

1010 12.1 100

12.1%

12.1

100

Self Check 3

UNIONSIn 2002, 13.3% of the

U.S. labor force belonged to a

union. Write this percent as a

fraction in simplest form.

Now TryProblems 27 and 31

EXAMPLE (^4) Write as a fraction in simplest form.
StrategyWe will drop the % symbol and write the given number over 100. Then
we will perform the division indicated by the fraction bar and simplify, if possible.
WHYWhen writing a percent as a fraction, the numerator and denominator of the
fraction should be whole numbers that have no common factors (other than 1).
Solution
66 Drop the % symbol and write 66 23 over 100.

2

3

%

(^66 23)
100

66 23 %

Self Check 4

Write 83 13 %as a fraction in

simplest form.

Now TryProblem 35