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Worked Example 4: Finding Missing Value

Part of Ratio Basics — GCSE Mathematics

This study notes covers Worked Example 4: Finding Missing Value within Ratio Basics for GCSE Mathematics. Revise Ratio Basics in Number for GCSE Mathematics with 12 exam-style questions and 22 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 10 of 14 in this topic. Use this study notes to connect the idea to the wider topic before moving on to questions and flashcards.

Topic position

Section 10 of 14

Practice

12 questions

Recall

22 flashcards

Worked Example 4: Finding Missing Value

If the ratio of boys to girls is 4:5 and there are 20 boys, how many girls are there?

Solution

Boys : Girls = 4 : 5

20 : ? = 4 : 5

Scale factor: 20 ÷ 4 = 5

Number of girls = 5 × 5 = 25

Answer: 25 girls

Keep building this topic

Read this section alongside the surrounding pages in Ratio Basics. That gives you the full topic sequence instead of a single isolated revision point.

Worked Example 3: Three-Way RatioWorked Example 5: Converting UnitsThe Art of SharingUnderstanding Ratios

Practice Questions for Ratio Basics

Write the ratio 12:18 in its simplest form.

  • A. 6:9
  • B. 4:6
  • C. 2:3
  • D. 3:2
1 markfoundation

Explain the difference between the ratio 3:5 and the ratio 5:3.

2 marksstandard

Quick Recall Flashcards

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'
Order in Ratios
Order MATTERS! Boys:Girls = 3:5 means: • 3 boys for every 5 girls Girls:Boys = 5:3 means: • 5 girls for every 3 boys Different meanings!

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Worked Example 3: Three-Way Ratio

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Worked Example 5: Converting Units