1. 8.4 Percent of Increase and Decrease

2. 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.

3. 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 decrease
original amount 4 16
Set up the ratio.

4. Reduce the fraction or find the decimal form. 4 16 1 4
Continued
Reduce the fraction or find the decimal form. 4 16 1 4 =
= 25% Write as a percent.
From 16 to 12 is a 25% decrease.

5. Is this percent an increase or decrease?
Try This:
Find the percent of increase or decrease from 15 to 20.
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 increase
original amount 5 15
Set up the ratio.

6. = 0.33… Find the decimal form.
Continued
Reduce the fraction if possible. 5 15
= 0.33… Find the decimal form. 1 3
= 33 1 % Write as a percent. 3 1
From 15 to 20 is a 33 % increase. 3

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

8. Percent Increase
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?
$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.