PERCENT OF CHANGE
SECTION 9.6
PERCENT OF CHANGE
• The percent a quantity
increases or decreases from its
original amount
• Percent of Change formula
Percent of Change
Step 1: Find the amount of
change by subtracting
Step 2: Plug in what you know.
Step 3: Cross Multiply
Step 4: Divide
Example
•
The number of participants in an athletic competition
increased from 312 to 351. Find the percent of increase.
Step 1: find the amount of change by subtracting
351 – 312 = 39
Step 2: Plug in what you know
amount of change x percent of change
original amount
100
Since we are looking for the percent of change, this becomes
your variable (unknown)
38
n
x
312
100
Step 3: Cross Multiply
38 x 100 = 312 x n
3800 = 312n
Step 4: Divide
3800 = 312n
312 312
12.18 = n
round your answer n = 12
Percent of increase is 12%
Example
•
With an adjustment in nutritional habits and exercise,
Jodi went from 190 pounds to a healthier 135 pounds.
What was the percent change in Jodi’s weight?
Step 1: Find the amount of change
190- 135 = 55
Step 2: Plug it into the formula
55
n
x
190
100
Step 3: Cross Multiply
5500 = 190n
Step 4: Divide
5500 = 190n
190
190
n = 28.95
round n = 29
Percent of decrease = 29%