With questions about proportion we use ratios in a slightly different way.

We are told a total amount and then we have to share it in a given ratio.

So perhaps there is £50 in total and we have to share it in the ratio 1:9 between Dasha and Masha.

The way to tackle a problem like this is to notice that there are 10 parts all together, so each part is equal to £50 ÷ 10, or £5.

Then we see that as Dasha has 1 part, she has £5 and as Masha has 9 parts, she has 9 x £5, or £45.

So the questions work a bit differently, although they still use ratios showing how things are shared between two or more people or things.

Sometimes, instead of being told the total amount, we are told the amount that one side of the ratio refers to. The process is similar but a little different,

So we could have been told that Dasha and Masha receive money in the ratio 2:7 and Dasha receives £10 and be asked how much Masha receives.

In this situation instead of dividing by 9 (why 9?) we would divide by 2 to see that 1 part is £5 and so Dasha receives 7 x £5 = £35

Worked Examples

Share $1 between Lasha and Sasha

The ratio of boys to girls in year 8 is 3:2. If there are 60 boys in year 8, then how many girls are there.

600ml is enough water to make 3 glasses of lemonade. How much water is needed to make 7 glasses of lemonade?

Exercise

Answers