Maths percentages %
- Write out what 100% is
- Write out what you know
- Keep % on one side then put the divide sign in
This method works for any % calculation.
A car is selling for £360 after a discount of 20%. Find the original price (x)
100% = x
80% = 360
Put the divide sign in to make:
What you do to one side, you do to the other, so multiplying both sides by 360 gives:
360 = 450
Therefore x (the original price) = £450
Harriet had £3500 in her savings account. After a year she has £3800. What % rate of interest did she have on her account?
3500 = 100%
3800 = x
It’s a good idea to keep x on top before you put the divide sign in, so that the equation will be:
Now multiply both sides by 100 to get x on its own:
3500 x 100
x = 108.57%
After a year Harriet had 108.57% of her original amount of £3500. Take away the original amount which is represented by 100% to find out the rate of interest:
108.57 – 100 = 8.57% per annum
Remember: this works for any percentage question.