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Ratio in context - OCRFinding 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

Explore the refreshed revision guide for GCSE Maths: Ratios, with step-by-step slideshows, quizzes, practice exam questions, and more!

Using a table can help to answer problems when one or more ratios 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 table using this information.

Boys (3)Girls (4)
2222
Boys (3)
Girls (4)
2
2
2
2

Because each part is equal, the rest of the table can now be filled in.

Boys (3)Girls (4)
2222222
Boys (3)
2
2
2
Girls (4)
2
2
2
2

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

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Scale factors
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Sharing in a given ratio

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