8.4 Percent of Increase and Decrease

Percent change is the ratio of the amount of change to the original amount.

Percent increase describes how much the original amount increases.

Percent decrease describes how much the original amount decreases.

amount of changeoriginal amountpercent change =

Find the percent increase or decrease from 16 to 12.

Is this percent an increase or decrease?

16 – 12 = 4 First find the amount of change.

Think: What percent is 4 of 16?

amount of decreaseoriginal amount

416

Set up the ratio.

Continued

= 25% Write as a percent.

Reduce the fraction or find the decimal form.

416

From 16 to 12 is a 25% decrease.

=14

Find the percent of increase or decrease from 15 to 20.

Try This:

Is this percent an increase or decrease?

20 – 15 = 5 First find the amount of change.

Think: What percent is 5 of 15?

amount of increaseoriginal amount

515

Set up the ratio.

Continued

= 33 1 % Write as a percent.

= 0.33… Find the decimal form.515

From 15 to 20 is a 33 % increase.

Reduce the fraction if possible.

13 3

31

Sarah bought a DVD player originally priced at $450 that was on sale for 20% off. What was the sale price?

Percent Decrease

$450 20% First find 20% of $450.

$450 0.20 = $90 20% = 0.20

The amount of decrease is $90.

Think: The reduced price is $90 less than $450.

$450 – $90 = $360 Subtract the amount of decrease.

The sale price of the DVD player was $360.

Mr. Olsen has a computer business in which he sells everything at 40% above the wholesale price. If he purchased a printer for $85 wholesale, what will be the retail price?

Percent Increase

$85 40% First find 40% of $85.

$85 0.40 = $34 40% = 0.40

The amount of increase is $34.

Think: The retail price is $34 more than $85.

$85 + $34 = $119 Add the amount of increase.

The retail price of this printer will be $119.