Transcript Document

Percent of Change
The percent that a value
increases or decreases
Vocabulary
(Section 5.7 in book)
• A percent of change is:
– a ratio that compares the change in a
quantity to the original amount.
•
For a percent of change, the proportion used is:
percentof change amountof change

100
originalamount
Ex 1) The Mitchell family bought a house several years
ago for $120,000. This year, they sold it for $150,000.
Find the percent of increase in the price of the house.
A percent of increase is a
percent of change.
Subtract the house values to
find the amount of change.
Use the starting price as the
original amount.
percentof change amountof change

100
originalamount
x  $150 ,000  $120 ,000
100
$120 ,000
x  $30,000
100 $120,000
120,000x  100(30,000)
x  25%
The price of the house increased by 25%.
Ex 2) Mercer Middle School had 240 students last year.
This year, there are 192 students enrolled. Find the
percent of change in the number of students. Is this a
percent increase or a percent decrease?
The percent of change is a
percent of decrease.
Subtract the number of students
to find the amount of change.
Use the earlier number of
students as the original amount.
percentof change amountof change

100
originalamount
x  240 192
100
240
x  48
100 240
240x  ( 48)100
x  20%
The number of students decreased by 20%.
Ex 3) The average speed of the winning
race cars in the Indy 500 are shown in
the table. Find the percent of change in
speed from 1955 to 2010. Round your
answer to the nearest whole percent.
The percent of change is a
percent of increase.
Subtract the speeds between
1955 and 2010 to find the
amount of change.
Use the average speed from
1955 as the original amount.
Year
Speed
(mph)
1922
94
1955
128
2010
162
percentof change amountof change

100
originalamount
x  162 128
100
128
x  34
100 128
128x  (34)100
x  27%
The average speed increased by approximately 27%.