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# Learner Guide

Ratio and proportion

Ratios are way to express the size of one part in comparison to other parts.

Proportions express the size of one part in comparison to the whole.

 Example 1.In this box of Lego bricks, there are 2 green bricks and 8 blue bricks. This means that    for every one green brick, there are four blue bricks. We can write this as a ratio of 1:4.  If we want to write the number of green bricks as a proportion, it is 2/10, which can be simplified to 1/5.

If you want to multiply something that has ratios, it is important to remember

that whatever is done to one of the parts must be done to all of the other parts.

 Example 2.A recipe for sponge cake has 100g flour, 2 eggs and 75g of sugar. As a ratio, we can write this as 100:2:75    Let’s say that we need to find out how much sugar we would need in a cake of the same ratios but with 300g of flour. The amount of flour has been tripled, so the other two parts must also be tripled.75 x 3 = 225 – the new cake would need 225g of sugar.

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