Definition: Percent change is the amount of increase or decrease in a quantity, written as a percent of the original amount.
What is percent change?
It measures how much something grew or shrank relative to where it started.
What is the formula?
Percent change = (new value – original value) / original value x 100. A positive result is an increase, and a negative result is a decrease.
How do you use it?
Mathbot’s gaming headset drops from 80 dollars to 62 dollars. The change is 62 – 80 = -18. Divide by the original: -18 / 80 = -0.225. So it is a 22.5 percent decrease.
What about finding a new amount?
Multiply by a factor. A 15 percent increase on 240 is 240 x 1.15 = 276. A 15 percent decrease is 240 x 0.85 = 204.
Why is the starting point important?
A 50 percent increase followed by a 50 percent decrease does not return to the start. From 100: 100 x 1.5 = 150, then 150 x 0.5 = 75.
What is a common mistake?
Dividing by the new value instead of the original value.
Where to learn it
- Calculating Percent Change and Percent Error – lesson
- Solving Multistep Percent Problems with Tax, Tips and Discounts – lesson