A ratio is a way of showing how two or more quantities are related. For example, if there are double the number of boys in a class compared with the number of girls, then we can show this by writing 2:1. This would be read as: 'the ratio of boys to girls is two to one'. Two parts of the class are boys and one part is girls, but: what is 'part(s) of' as a fraction? It's easy: 2 + 1 = 3, so 2⁄3 are boys, and 1⁄3 is girls. You would deal with other ratios in a similar way.
Be warned: if you reverse the order of the numbers in a ratio, the ratio changes. 2:1 is NOT the same as 1:2. The order in which you write your ratio is important. Finally, ratios can be simplified by dividing/multiplying the ratio by another number, e.g. 4:8 can be written as 1:2 by dividing both numbers in the ratio by 4.
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