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Ratio
Introduction
A ratio is a way of comparing two or more quantities. For example, if a dog
weighs 8kg and a cat weighs 4kg then the dog weighs twice as much as the cat.
The ratio of the weight of the dog to the weight of the cat is 2 to 1. Note that the
two weights are in the same units. In this example the weights are in kg. If the
units are not the same then you should convert, so that they are the same before
calculating the ratio.
You can use ratio to compare more than two quantities. If a goat weighs 24kg it
is three times the weight of the dog. The ratio of the goat to the dog is 3 to 1.
The ratio of the goat to the cat is 6 to 1. The ratios of the weights of the goat,
dog and cat are 6 to 2 to 1.
In the examples, the minimum working required is highlighted in blue.
Example 1
Three lines measure 3cm, 4cm and 5cm. What are the ratios of the lengths?
They are all in centimetres and so the unit is not included. The ratios are 3 to 4
to 5. A colon symbol is used to show a ratio and so the ratios 3 to 4 to 5 are
written:
3:4:5
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