# Maths Revision : Understanding Ratios

**Ratios:** A ratio is a way of comparing the sizes of two (or more) quantities. Colons are used when expressing ratios, so that the values of A and B being in the ratio 2 to 5 would be written as A : B = 2 : 5. [NB: In some older text books, :: is used here, i.e. A : B :: 2 : 5.]

If you multiply/divide one side of a ratio then you must multiply/divide the other side of the ratio by the same amount.

To divide a total in a given ratio you must first add the separate parts of the ratio to get the total amount, which is divided into each part of the ratio to get a fraction of the total amount.