Warm Up
1. 14,000 is 2 1
2% of what number? 560,000
2. 39 is 13% of what number?
300
3. 37 1% of what number is 12?
32
2
4. 150% of what number is 189?
126
Lesson 2
Percent Increase and Decrease
Percents can be used to describe a
change. Percent of change is the ratio of
the amount of change to the original
amount.
percent of change =
amount of change
original amount
Percent of increase describes how much
the original amount increases.
Percent of decrease describes how much
the original amount decreases.
Class Example
Find the percent of increase or decrease from
16 to 12.
This is a percent of decrease.
16 – 12 = 4
First find the amount of change.
amount of decrease
original amount
4 = 0.25 = 25%
16
4
Set up the ratio.
16
Find the decimal form.
Write as a percent.
From 16 to 12 is a 25% decrease.
Partner Practice
Find the percent increase or decrease from
45 to 54.
This is a percent of increase.
54 – 45 = 9
First find the amount of change.
amount of increase
original amount
9 = 0.20 = 20%
45
9 Set up the ratio.
45
Find the decimal form.
Write as a percent.
From 45 to 54 is a 20% increase.
Individual Practice
Find the percent increase or decrease from
50 to 65.
This is a percent of increase.
65 – 50 = 15
First find the amount of change.
amount of increase
original amount
15 = 0.30 = 30%
50
15 Set up the ratio.
50
Find the decimal form.
Write as a percent.
From 50 to 65 is a 30% increase.
Class Example
When Jim was exercising, his heart rate
went from 72 beats per minute to 98 beats
per minute. What was the percent increase
to the nearest tenth of a percent?
98 – 72 = 26
First find the amount of change.
amount of increase
original amount
26
72
Set up the ratio.
26  0.361  36.1%
Find the decimal form.
72
Write as a percent.
From 72 to 98 increases by about 36.1%.
Individual Practice
In 2005, a certain stock was worth $1.25 a
share. In 2006, the same stock was worth
$0.85 a share. What was the percent
decrease?
1.25 – 0.85 = 0.40
amount of decrease
original amount
First find the amount of change.
0.40
1.25
Set up the ratio.
Find the decimal form.
0.40
= 0.32 = 32% Write as a percent.
1.25
The value of the stock decreased by 32%.
Discount is the difference between the
regular price and the sale price of an item.
You can use percent of decrease to find
discounts.
Markup is the difference between the
wholesale cost and the retail price of an
item. You can use percent of increase to
find markups.
Practice
Sarah bought a DVD player originally priced at
$450 that was on sale for 20% off. What was
the discounted price?
Method 1: Multiply, then subtract.
(450)(0.20) = 90
Find 20% of $450. This is
the amount of discount.
450 – 90 = 360
Subtract $90 from $450.
Method 2: Subtract, then multiply.
100% – 20% = 80% Find the percent Sarah pays.
(450)(0.80) = 360
Find 80% of 450.
The discounted price was $360.