Understanding ratio
A ratio shows the relationship between two quantities.
It is written in the form a:b which is read as ‘a to b’.
Example
John has a pack of sweets. He shares them with a friend in the ratio 3:2. This means that for every 3 sweets John eats, he gives his friend 2.
If John eats 15 sweets (5 × 3), his friend will receive 10 sweets (5 × 2).
In the example, this means that John has 5 lots of 3 sweets so his friend will have 5 lots of 2 sweets.
Question
Bread is made using 5 parts of flour to 3 parts liquid.
a) Write down the ratio of liquid to flour.
b) If the recipe calls for 200 g of flour, how much liquid will be needed?
a) 3:5
As the question asks for the ratio of liquid to flour, you must write the number of parts of liquid first, followed by flour.
b) 5 parts = 200
1 part = 200 ÷ 5 = 40
3 parts = 3 × 40 = 120
120 ml of liquid will be needed.
Question
Cookies are made using the ratio 3:2:1 of flour, fat and sugar.
If a recipe calls for 150 g of flour, how much fat and sugar are needed?
3 parts = 150 g
Divide 150 by 3 to find what 1 part is worth
1 part = 50 g
Fat = 2 parts = 2 × 50 = 100 g
Sugar = 1 part = 50 g
