1. 8.4 Percent of Increase and Decrease

2. Percent increase describes how much the original amount increases.
Percent change is the ratio of the amount of change to the original amount.
amount of change
original amount
percent change =
x 100
Percent increase describes how much the original amount increases.
Percent decrease describes how much the original amount decreases.

3. Finding Percent of Change
20 is decreased to 11
20 – 11 = 9
Percent of Change = amount of change
original amount
Percent of Change = 9 20
Percent of Change ≈ 0.45
Percent of Change ≈ 45%

4. Finding Percent of Change
32 is increased to 67
68 – 32 = 36
Percent of Change = amount of change
original amount
Percent of Change = 36 32
Percent of Change ≈
Percent of Change ≈ 112.5%

5. Finding Percent of Change Word Problems: Your Turn
Angela is a famous architect. She made $90,000 in In 2005 she made $120,000. What is the percent of increase?

6. What percent did the prices change for the Cell phone?
Prices at a local electronic store have changed over the years. By what percent did the prices increase or decrease for the stereo system?
What percent did the prices change for the Cell phone?
Item
1994
2004
Stereo
System
$98.95
$135.95
Cell Phone
$245
$159

7. Lesson Quiz for Student Response Systems
1. Identify the percent increase or decrease to the nearest percent.
from 23 to 29
A. 26% decrease
B. 26% increase
C. 32% decrease
D. 32% increase 7

8. Lesson Quiz for Student Response Systems
2. Identify the percent increase or decrease to the nearest percent.
from 1440 to 1220
A. 15% decrease
B. 15% increase
C. 28% decrease
D. 28% increase 8

9. Lesson Quiz for Student Response Systems
3. A winter coat originally sold for $75 but is now on sale for 20% off. What is the sale price of the winter coat?
A. $55
B. $60
C. $65
D. $70 9

10. Lesson Quiz
Find each percent increase or decrease to the nearest percent.
1. from 12 to 15
2. from 1625 to 1400
3. from 37 to 125
4. from 1.25 to 0.85
5. A computer game originally sold for $40 but is now on sale for 30% off. What is the sale price of the computer game?
25% increase
14% decrease
238% increase
32% decrease
$28