Pie Chart
Competitive Mathematics · Data Interpretation
Cut a whole cake into slices — a bigger slice is a bigger share. A pie chart is exactly that: the whole circle stands for a total and each sector is one part of it. The sector’s angle, its arc length and its area are all proportional to the share. So pie-chart questions are a game of three things: percent, angle and actual value.
Reading a pie chart
Converting between a sector’s percent, angle and actual value.
Three forms, one share
Reading a pie sector as a percent, an angle or a value.
A student’s 24 hours are shown in the pie chart (the sectors are given as angles).
- **The full circle = = 100% = the total.** So and .
- Angle to percent: ; percent to angle: .
- Actual value = (angle ÷ 360) × total = (percent ÷ 100) × total.
- The **angles must add up to ** (the percents to 100) — a check, and also a way to find a missing sector.
- 1Study angle : hours .
- 2Percent
- 1Sleep: hours.
- 2Play + others hours; difference hours
Pie chart: Distribution of a family’s monthly income. monthly income: ₹ 60,000. Study the chart and answer (the sectors are given as percents of the total).
Pie chart: Results of the students in an examination. total students: 480. Study the chart and answer (the sectors are given as central angles; the full circle is ).
Comparing the parts
Comparing two or more sectors, finding the total and comparing with the average.
Rules for comparison
Rules for comparing the sectors within one pie chart.
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Two charts and change
Comparing two pie charts (two years or cities) and questions where the total changes.
Comparing two pie charts
When the two charts have different totals.
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Traps and fast tricks
Where marks go in pie-chart questions.
The commonest mistakes
The slips that cost marks.
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Fast tricks
Habits for speed.
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The practice ladder
New pie charts and questions of every type, in three levels.
Level 1 — Basic
One-step questions.
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Level 2 — Standard
Exam-level questions.
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Level 3 — Advanced
Questions at the hard end of competitive exams.
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Revision — formula cards
Read the front, think, then flip.
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