Basic Mathematics for College Students

There are many situations in our daily lives that call for rounding amounts of

money. For example, a grocery shopper might round the unit cost of an item to the

nearest cent or a taxpayer might round his or her income to the nearest dollar when

filling out an income tax return.

324 Chapter 4 Decimals

EXAMPLE 9

a.Utility Bills A utility company calculates a homeowner’s monthly electric

bill by multiplying the unit cost of $0.06421 by the number of kilowatt hours

used that month. Round the unit cost to the nearest cent.

b.Annual Income A secretary earned $36,500.91 dollars in one year. Round

her income to the nearest dollar.

StrategyIn part a, we will round the decimal to the nearest hundredth. In part b,

we will round the decimal to the ones column.

WHYSince there are 100 cents in a dollar, each cent is of a dollar. To round to

the nearest centis the same as rounding to the nearest hundredthof a dollar. To

round to the nearest dollaris the same as rounding to the ones place.

Solution

a.The rounding digit in the hundredths column is 6. Since the test digit 4 is less

than 5, we round down.

Rounding digit: Keep the rounding digit:

hundredths column Do not add 1.

$0.06421 $0.06421

Test digit: 4 is less than 5. Drop the test digit and

all digits to the right.

Thus, $0.06421 rounded to the nearest cent is $0.06.

b.The rounding digit in the ones column is 0. Since the test digit 9 is 5 or greater,

we round up.

Rounding digit: ones column Add 1 to 0.

$36,500.91 $36,500.91

Test digit: 9 is 5 or greater. Drop the test digit and

all digits to the right.

Thus, $36,500.91 rounded to the nearest dollar is $36,501.

1

100

Self Check 9

a.Round $0.076601 to the

nearest cent

b.Round $24,908.53 to the

nearest dollar.

Now TryProblems 85 and 87

Year Pounds

1960 2.68

1970 3.25

1980 3.66

1990 4.50

2000 4.64

2007 4.62

(Source: U.S. Environmental

Protection Agency)

7 Read tables and graphs involving decimals.

The table on the left is an

example of the use of decimals. It

shows the number of pounds of

trash generated daily per person

in the United States for selected

years from 1960 through 2007.

When the data in the table is

presented in the form of a bar

graph,a trend is apparent. The

amount of trash generated daily

per person increased steadily

until the year 2000. Since then, it

appears to have remained about

the same.

0.5

1.0

1.5

2.0

2.5

3.0

1960 1970 1980

Year

Pounds

1990 2000

3.5

4.0

4.5

5.0

2007

2.68

3.25

3.66

4.50 4.64 4.62

Pounds of trash generated daily (per person)