Pie charts
Objective. Construct and interpret pie charts using proportional angles.
- 1. Learn
- 2. Worked example
- 3. Practice
- 4. Feedback
- 5. Continue
Learn: the key idea
A pie chart shows categorical data as sectors of a circle, where each sector's angle is proportional to the frequency it represents out of the whole 360°. To find the angle for a category, divide its frequency by the total frequency, then multiply by 360°. Example: if 15 out of a total of 60 people chose a category, the angle is (15 ÷ 60) × 360° = 90°. When interpreting a pie chart, the reverse process converts an angle back into a proportion or frequency using the same ratio.
Worked example
In a survey of 60 pupils, 15 chose football. What angle does football get on a pie chart?
- 1A full pie chart is 360°.
- 2Football is 15 out of 60 pupils, which is 15/60 = 1/4.
- 3Angle = 15/60 × 360°.
- 4Angle = 90°.
Answer: 90°
Concept mastery
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Practice
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Start practisingCommon mistake. Pupils sometimes forget to multiply by 360° and leave the answer as just a fraction of the total; always complete the calculation by multiplying the proportion by 360° to get a correct angle in degrees.
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