Percent Increase and Decrease
How do you use percents
to describe change?
Find Percent Change
Percent Change = Describes how an amount
changes (Change can be an increase or
decrease).
Percent Change =
𝑎𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑖𝑛𝑐𝑟𝑒𝑎𝑠𝑒 𝑜𝑟 𝑑𝑒𝑐𝑟𝑒𝑎𝑠𝑒
𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝑎𝑚𝑜𝑢𝑛𝑡
Algorithm to Find Percent Change
1) Write Percent Change Formula
∗ 𝑎𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑖𝑛𝑐𝑟𝑒𝑎𝑠𝑒 𝑜𝑟 𝑑𝑒𝑐𝑟𝑒𝑎𝑠𝑒
𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝑎𝑚𝑜𝑢𝑛𝑡
2) Substitute Values & Simplify
*Amount of Increase or Decrease = Greater Value – Lesser Value
3) Divide (at least until thousandths place)
4) Rewrite decimal as a percent and round (if
needed)
Examples:
1) The number of students in a chess club
decreased from 18 to 12. What is the percent
decrease? Round to the nearest percent.
2) The officer wrote 10 tickets last week, but 16
tickets this week. What is the percent increase?
Round to the nearest percent.
Using Percent Change to
Find New Amount
Given an original amount and a percent change,
you can find the new amount:
1) Find amount of change
Amount of Change = Original Amount • Percent Change(*)
*
Cannot multiply by percent; Rewrite percent as a decimal, then multiply.
2) Find new amount
New Amount = Original Amount +/- Amount of Change
*If Amount is increasing, add Amount of Change
*If Amount is decreasing, subtract Amount of Change
Examples:
1) A tv has an original price of $499. Find the
new price after the given percent change.
a. 10% increase
b. 30% decrease