1. Learn to find percent increase and decrease.

2. Vocabulary
percent change
percent increase
percent decrease

3. Percents can be used to describe a change
Percents can be used to describe a change. Percent change is the ratio of the amount of change to the original amount.
amount of change
original amount
percent change =
Percent increase describes how much the original amount increases.
Percent decrease describes how much the original amount decreases.

4. Additional Example 1: Finding Percent Increase or Decrease
Find the percent increase or decrease from 16 to 12.
This is percent 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.

5. Additional Example 1 Continued4 16
= Find the decimal form.
= 25% Write as a percent.
From 16 to 12 is a 25% decrease.

6. Check It Out: Example 1
Find the percent increase or decrease from 15 to 20.
This is percent increase.
20 – 15 = 5 First find the amount of change.
Think: What percent is 5 of 20?
amount of increase
original amount 5 20
Set up the ratio.

7. Check It Out: Example 1 Continued5 20
= Find the decimal form.
= 25% Write as a percent.
From 15 to 20 is a 25% increase.

8. Additional Example 2A: Life Science Application
When Jim was exercising, his heart rate went from 70 beats per minute to 98 beats per minute. What was the percent increase?
98 – 70 = 28 First find the amount of change.
Think: What percent is 28 of 70?
amount of increase
original amount 28 70
Set up the ratio.

9. Additional Example 2 Continued
= 0.4 Find the decimal form. 70 28
= 40% Write as a percent.
Jim’s heart rate increased by 40% when he exercised.

10. Additional Example 2B: Application
In 1999, a certain stock was worth $1.25 a share. In 2002, the same stock was worth $0.85 a share. What was the percent decrease?
1.25 – 0.85 = 0.40 First find the amount of change.
Think: What percent is 0.40 of 1.25?
amount of decrease
original amount
1.25
0.40
Set up the ratio.

11. Additional Example 2B Continued
1.25
0.40
= Find the decimal form.
= 32% Write as a percent.
The value of the stock decreased by 32%.

12. Check It Out: Example 2A
When Jeff was watching TV, the number of times his eyelids blinked went from 50 blinks per minute to 75 blinks per minute. What was the percent increase?
75 – 50 = 25 First find the amount of change.
Think: What percent is 25 of 50?
amount of increase
original amount 25 50
Set up the ratio.

13. Check It Out: Example 2A Continued
= 0.5 Find the decimal form. 50 25
= 50% Write as a percent.
The blinking of Jeff’s eyelids increased by 50% when he watched TV.

14. Check It Out: Example 2B
In 2000, a certain stock was worth $9.00 a share. In 2003, the same stock was worth $3.80 a share. What was the percent decrease, to the nearest tenth?
9.00 – 3.80 = 5.20 First find the amount of change.
Think: What percent is 5.20 of 9.00?
amount of decrease
original amount
9.00
5.20
Set up the ratio.

15. Check It Out: Example 2B Continued
9.00
5.20
= Find the decimal form.
= 57.7% Write as a percent.
The value of the stock decreased by about 57.8%.

16. Additional Example 3A: Using Percent Change to Find Discounts and Markups
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.

17. Additional Example 3B: Using Percent Change to Find Discounts and Markups
Mr. Olsen has a computer business in which he marks everything up 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.

18. Check It Out: Example 3A
Lily bought a dog house originally priced at $750 that was on sale for 10% off. What was the sale price?
$750  10% First find 10% of $750.
$750  0.10 = $75 10% = 0.10
The amount of decrease is $75.
Think: The reduced price is $75 less than $750.
$750 – $75 = $675 Subtract the amount of decrease.
The sale price of the dog house was $675.

19. Check It Out: Example 3B
Barb has a grocery store in which she sells everything at 50% above the wholesale price. If she purchased a prime rib for $30 wholesale, what will be the retail price?
$30  50% First find 50% of $30.
$30  0.50 = $15 50% = 0.50
The amount of increase is $15.
Think: The retail price is $15 more than $30.
$30 + $15 = $45 Add the amount of increase.
The retail price of the prime rib will be $45.