One Quantity as a Percentage of Another

One Quantity as a Percentage of Another

GCSE(F),

To calculate the percentage of an amount, turn the percentage into a fraction (by dividing by 100), then carry out the calculation:

38% of 420

= `frac(38)(100)` x 420

= 0.38 x 420

= 159.6

Examples

1. A saver ticket works out at 70% of the cost of a full price ticket. If a full price ticket is £130, what is the saver ticket price?

Answer: £91

70% x 130

= `frac(70)(100)` x 130

= 0.7 x 130

= 91

2. A car is purchased for £8000. Three years later it is sold for £6500. What percentage was the sold price compared to the original price? Give your answer to 2 significant figures.

Answer: 81%

The result can be worked out from:

6500 = 8000 x x, where x is the decimal equivalent of the percentage

`frac(6500)(8000)` = x

x = 0.8125

Multiply by 100 to change the decimal to a percentage:

0.8125 x 100 = 81.25% = 81% (2sf)