Ratio Basics

MathematicsAQAEdexcelGCSEUnit: Number
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The basics

The Art of Sharing

The Art of Sharing

From mixing paint colors to baking the perfect cake, ratios are everywhere. When a recipe calls for flour to sugar in the ratio 3:1, or when artists mix yellow and blue paint in ratio 2:3 to get the perfect green, they're using one of mathematics' most practical tools. Ratios help us understand proportions, scale models, map distances, and financial splits - making fair sharing and accurate scaling possible in countless real-world situations.
What is a ratio?: A comparison of quantities of the same kind Written as a:b or a/b Example: 3:5 means '3 parts to 5 parts'
Key terms

Mathematics glossary

What is a ratio?
A comparison of quantities of the same kind Written as a:b or a/b Example: 3:5 means '3 parts to 5 parts'
Exam tip

Earn the mark scheme marks

Common Mistakes to Avoid

❌ Wrong: Adding to ratios: 2:3 + 1:2 = 3:5 ✅ Right: Cannot add ratios directly

Convert to fractions or find common format first

❌ Wrong: Ignoring order: 3:5 same as 5:3 ✅ Right: Order matters in ratios

3:5 means first is 3 parts, second is 5 parts

❌ Wrong: Not converting units: 2m : 50cm = 2:50 ✅ Right: 200cm : 50cm = 4:1

Always convert to same units before simplifying

❌ Wrong: Forgetting to simplify: Answer 10:15 ✅ Right: 10:15 = 2:3

Always give ratio in simplest form

Now try it yourself

Quiz · Question 1 of 12

Write the ratio 12:18 in its simplest form.

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