Ratio in context - EdexcelFinding unknown ratios

Ratios are seen in everyday life. They can be used when adding ingredients to make a meal, when deciding how much pocket money children get or when reading a map.

Part ofMathsRatio, proportion and rates of change

Finding unknown ratios

Using a diagram can help to answer problems when one or more are incomplete or unknown.

Example

Some boys and girls are divided into teams in the ratio \(3:4\). There are 8 girls in one team. How many boys are there in the team?

There are 8 girls shared into 4 parts. Each part has \(\frac{8}{4} = 2 \:\text{girls}\).

Fill in the diagram using this information.

A ratio diagram to help work out the ratio of boys to girls in the ratio of 3:4. Boy’s boxes are blank and the girl’s contain 4 sets of 2.

Now because the amounts are shared equally between all of the parts, the rest of the diagram can be filled in.

A completed ratio diagram to show the ratio of boys to girls in the ratio of 3:4. Boys boxes contain 3 sets of 2 and the girls contain 4 sets of 2.

From the diagram it is clear that the number of boys in the team is \(2 \times 3 = 6\).

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Scale factors
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Sharing in a given ratio

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