6th Grade Math Textbook, Fundamentals

 &KDSWHU

7-9

Percent Decrease

Objective To find the percent decrease• To find the selling price for an item sold at a loss

In the first modern Olympic Games in 1896, the
winning time in the men’s 100-meter sprint was
12 seconds. By the 2004 games, the winning time
had dropped to 9.85 seconds. To the nearest tenth
of a percent, what is the percent decrease in the
winning time from 1896 to 2004?

To find the for the winning time
from 1896 to 2004, compare the amount of decrease
to the original amount.

You can use the formula for rate of decrease,

or you can use a proportion to find the

percent decrease.

Method 1 Write an Equation

percent decrease 

Let RDthe percent decrease.

RD

RD Divide to simplify.

RD0.17916 Multiply by 100 to rename the decimal as a percent.

RD17.9% Round to the nearest tenth of a percent.

Method 2 Write and Solve a Proportion

Let nthe unknown percent decrease.

12 9.85 2.15





2.15 • 100  12 n

 Divide both sides by 12

n17.916

n17.9 Round to the nearest tenth.

So the percent decrease in the winning time for the men’s 100-meter sprint

from 1896 to 2004 is approximately 17.9%.

percent decrease

part

whole

12 n

12

215

12

Substitute 2.15 for the amount of decrease and

12 for the original amount, then cross multiply.

n

100

2.15

12

Subtract the original amount from the new

amount to find the amount of decrease.

amount of decrease

original amount

percent decrease (%)

100

2.15

12

12 9.85

12

amount of decrease

original amount

Subtract the new amount from the original amount to find the

amount of decrease. Substitute 12 for the original amount and

9.85 for the new amount.

Remember:

percent change 

amount of change

original amount