Percent of Change
1.
What is 20% of 70?
2.
What percent of 24 is 18?
3.
32 is 10% of what number?

Percent of Change:
The percent a quantity increases or decreases
compared to the original amount.

Increase:
Goes up, gets bigger, gets larger, grows, more

Decrease:
Goes down, gets smaller, shrinks, less
Amount of change:

Try this on your calculator
18 – 10
=8
10 – 18
=–8
Went down 8
Went up 8
You can tell if they went up or down without a
calculator, so just ignore the negative & use 8 either
way.
?
amount of change

100
original amount
?
start - finish

100 original amount
Ignore negatives or use absolute value!
The amount of change is the absolute value of the difference between the new amount
and the original amount.
Find the % of change from $10 to $18
?
18 – 10
=
100
10
?
8

100 10
Solve:
8 100 10
= 80
Going from $10 to $18 is an 80% increase
Example 1
Example 1
2
Find the percent of decrease from 25 to 21
?
25 – 21
=
100
25
?
4

100 25
Solve:
4 100  25
= 16
Going from 25 to 21 is a 16% decrease
Identify the percent of change as an increase or a
decrease. Find the percent of change. Round percents
to the nearest tenth if necessary.
1.
4 to 5
2.
20 to 16
3.
12 to 6
Find the percent of decrease from 25 to 21.

Calculate the amount of decrease.

Calculate the percent of decrease.
25 – 21 = 4
amount of decrease 4

 0.16  16%
original amount
25

The percent of decrease from 25 to 21 is 16%.
Last year 2300 people attended a Fourth of July parade at the beach. This year the
number of people increased by 8%. Find the number of people who attended the
parade this year.
amount of increase
Percent of increase 

Use the percent of change equation.
original amount
x
2300

Write the percent as a decimal.
0.08 

Multiply both sides by 2300.
184 = x

There were 184 more people this year.

Add to last year’s number for total.

There were 2,484 people at the parade this year.
2300 + 184 = 2484
Do you think there has been a percent increase or a
percent decrease in the total number of students in your
school compared to ten years ago? Why?
Targets:
Find the percent of increase or the percent of decrease between two numbers.
Use percent of change to find new values.
Example 1
Find the percent of increase from 10 to 18.

Calculate the amount of increase.

Calculate the percent of increase.
18 – 10 = 8
amount of increase
8
  0.8  80%
original amount
10

The percent of increase from 10 to 18 is 80%.
In 1999, Hernandez paid $2,000 for a new laptop computer. In 2007, Hernandez
paid 60% less for a laptop computer than he had in 1999. Find the amount he paid
in 2007.
amount of decrease
Percent of decrease 

original amount
Use the percent of change equation.
x
2000

Write the percent as a decimal.
0.6 

Multiply both sides by 2,000.
1200 = x

Hernandez paid $1,200 less in 2007 than in 1999.

Subtract 1200 from the value in 1999.

Hernandez paid $800 for a laptop computer in 2007.
2000 – 1200 = 800