Percentage change
Sometimes prices, volumes and other quantities are increased or decreased by a percentage of the original amount. It is useful to be able to calculate the percentage change and the new amount.
One straightforward way to do this is in three steps.
Increasing or decreasing by a given percentage
- Calculate one percent
- Calculate the percentage given
- Add or subtract the percentage as required
Example
A landlord raises his rental prices by 5%. How much will rent priced at 拢350 a month cost after the increase?
Answer
- 1% of 拢350 = 拢3.50
- 5% = 5 x 拢3.50 = 拢17.50 (this is the amount of increase)
- 拢350 + 拢17.50 = 拢367.50
The new rent is 拢367.50 per month.
Question
A shop reduces all their stock by 15%. How much would a jacket, costing 拢60, now cost in the sale?
- 1% of 拢60 = 拢0.60
- 15% = 15 x 拢0.60 = 拢9 (this is the amount of decrease)
- 拢60 - 拢9 = 拢51
The sale price of the jacket is 拢51.