Ratio is used to indicate how much of one thing there is compared to another. When talking about ratio it is a good idea to use the word PART with it, such as ‘one part juice to 5 parts water’. Then a part might be a cup, a litre, or a jugful. See how well you can work with ratio in this GCSE Maths quiz.

One of the key things about ratio is that it doesn’t include units, and so can be applied to a variety of situations. Replace the word ‘part’ with whatever unit you want – as long as you are consistent, you will mix things in the right ratio. Ratio is most commonly written using a colon to separate the two (or more) things, such as 1:5. We would read this as ‘1 part to 5 parts’.

Just like fractions, ratios can be cancelled down and written in their simplest form, by dividing each number by the Highest Common Factor (HCF).

Another way you may be asked to write a ratio is in the form 1:n. In this case, ask yourself what you need to divide the left-hand side by to get to 1 (it will be itself), and do the same to the right-hand side. This is particularly useful if it is going to be scaled up in the future.

You need to know how to divide a quantity up into a given ratio. These are the trickiest type of ratio questions, but with a little bit of thought they don’t have to be. The key here is to ask yourself how many parts in total, and then work out the value of 1 part. So, if £25 is to be split in the ratio 2:3, there are 5 parts in total, so each part is worth £5. The money would be split £10 to £15.

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