Maths percentages %

1. Write out what 100% is
2. Write out what you know
3. Keep % on one side then put the divide sign in

This method works for any % calculation.

Example 1

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:

 100
80  = x
360                                                    

What you do to one side, you do to the other, so multiplying both sides by 360 gives:

360 x 100
80= 360x
360 = 450                          

Therefore x (the original price) = £450

Example 2

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:

3800
3500 = x
100         

Now multiply both sides by 100 to get x on its own:

x =3800
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.