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Tips for ratio and proportion

A ratio can be written as a number of parts. It can also be written using a symbol.

Example: 1 part to 3 parts is written 1:3.

The order in a ratio in important.

Example: 5 parts sand to 1 part cement is 5:1. 1:5 would mean 1 part sand to 5 parts cement - a very different mix.

To mix a total amount from different ingredients in a given ratio, first work out the total number of parts. Then write each part as a fraction. Then find that fraction of the total amount you want to make.

Example: Make 2 litres of squash by mixing 1 part orange to 3 parts water.
Total numbers of parts = 1 + 3 = 4
Orange is 1 part out of 4, that's ¼ . ¼ of 2 litres = 0.5 litres
Water is 3 parts out of 4, that's ¾ . ¾ of 2 litres is 1.5 litres.

To adapt a recipe for a different number of servings, you need to increase or decrease the amount of each ingredient by the same proportion.

To increase quantities, multiply the quantity of each ingredient by the same number.
To decrease quantities, divide the quantity of each ingredient by the same number.
Look out for numbers where the increase is 'half as much again', for example from 2 to 3, from 4 to 6, from 20 to 30.