Data Interpretation • Topic 3 of 6

Pie Charts

A pie chart shows how a whole is divided into parts, each slice a percentage of the total. The percentages always add to 100. To find how many items a slice represents, multiply its percentage (as a decimal) by the total: a 40% slice of 600 is 0.40 × 600 = 240. To find a slice’s central angle, multiply its percentage by 360°, since the whole circle is 360°. The frequent mistake is treating the percentage itself as the count. Always check whether the question wants a count, a percentage, an angle, or a fraction of the whole.

A pie chart with slices of 40, 25, 20 and 15 percentPie chart40%25%20%15%

✅ Solved examples

1. A pie chart: Bus 40% of 600 students. How many take the bus?
0.40 × 600 = 240.
2. A 25% slice — what is its central angle?
0.25 × 360° = 90°.
3. A pie chart shows Rent 30% of a $2,000 budget. How much is rent?
0.30 × 2000 = $600.
4. If three slices are 20%, 35% and 25%, what percent is the fourth?
100 − 20 − 35 − 25 = 20%.

✏️ Practice — try these, take hints as needed

1. A 20% slice of 500 books — how many books?
Multiply percent (as decimal) by total.
0.20 × 500.
—
100.
2. What central angle matches a 50% slice?
Percent × 360°.
0.50 × 360.
—
180°.
3. A pie chart: Food 25% of a $1,200 budget. How much on food?
0.25 × 1200.
—
—
$300.
4. Slices are 45%, 30% and the rest. What percent is the rest?
They sum to 100%.
100 − 45 − 30.
—
25%.
5. A 10% slice of 800 visitors — how many visitors?
0.10 × 800.
—
—
80.

📝 Topic test — 8 questions

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