Reverse Percentage
Reverse percentage (or working backwards from a percentage) lets us find the original value before a percentage increase or decrease was applied.
What You Need to Know
Key Concept Diagram
If a value has been increased by r%, the multiplier is (1 + r/100); divide by this to reverse
If a value has been decreased by r%, the multiplier is (1 - r/100); divide to find the original
Always identify what 100% represents before calculating
Reverse percentage is used in tax, discounts, and price markups
Key Vocabulary
Multiplier
The decimal used to apply a percentage change (e.g. 1.2 for a 20% increase)
Reverse percentage
Finding the original value before a percentage change was applied
Original value
The starting amount before any percentage increase or decrease
GST
Goods and Services Tax; in Australia, 10% is added to most prices
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
A shirt costs $66 after a 10% GST is added. What was the original price?
Question 2
A laptop was discounted by 20% and now costs $480. What was the original price?
Question 3
Which calculation finds the original price when a 15% increase has been applied?
Key Concepts Summary
- ●If a value has been increased by r%, the multiplier is (1 + r/100); divide by this to reverse
- ●If a value has been decreased by r%, the multiplier is (1 - r/100); divide to find the original
- ●Always identify what 100% represents before calculating
- ●Reverse percentage is used in tax, discounts, and price markups