How do I work out a reverse percentage?
By Garret Patton on the 11th of June, 2012
A reverse percentage is when you are given a percentage question and have to work backwards.
You will be given a number that has already been increased/decreased and have to work out what the original number was.В
To solve it remember that the original amount is 100%. From this point work out what percentage the amount you are given is and then find the 100% from mulitplication and division.В
A lamp is sold for ВЈ18 after a 10% decrease. Find out the original price of the lamp.
So the original price = 100%
This means that the lamp sold for 90% of the full price.
So if ВЈ18 is 90% then 100% is given by 18x(10/9) = 20.
So the original price is ВЈ20.В
Refine By Lee Mansfield on the 13th of June, 2012
Work out reverse percentage problems
The usual question here has to do with sales discounts. For example, a coat is on offer, 25% off. Its sale price is ВЈ200. What was the original price before the reduction?
The mistake most people make is find 25% of ВЈ200 (ВЈ50), add it on, and then say that was the original price: ВЈ250.
This is WRONG!
25% was taken off the original price, which was higher than ВЈ200. That means the reduction was more than just fifty quid. There are two ways to work out what the original price was. One is the unitary method (also used when calculating with ratios). The other is much simpler if you have a calculator to hand, but less intuitive.
Unitary method вЂ“ the original price was 100%, and the sale price is 75% of the original.
- 100% Original Price ? 75% Sale Price ВЈ200