Reading Pie Charts

Pie charts appear in roughly 1 out of 9 QR data sets. They show how a total is divided into parts, with each slice representing a proportion. Pie chart questions typically require you to calculate absolute values from percentages, compare slices, or work backwards from a known value to find the total.

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How Pie Charts Present Data

A pie chart represents a whole (100%) divided into segments (slices). Each segment's size is proportional to the quantity it represents.

Pie charts in QR may show:

• Percentage labels on each segment (e.g., 25%, 15%, 35%, 25%)
• Degree labels (e.g., 90°, 54°, 126°, 90° — adding to 360°)
• Value labels (e.g., £2,500, £1,500, £3,500, £2,500)
• No labels — requiring you to estimate segment sizes

The total is usually given separately — either in the title, a caption, or the question itself.

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Converting Between Degrees, Percentages, and Values

Degrees to Percentage

Since a full circle is 360°:

Percentage = (Degrees ÷ 360) × 100

Degrees	Percentage
36°	10%
72°	20%
90°	25%
108°	30%
120°	33.3%
144°	40%
180°	50%

Percentage to Value

Value = (Percentage ÷ 100) × Total

Example: A pie chart shows that 35% of a school's 1,200 students study French.

Number studying French = 35% × 1,200 = 0.35 × 1,200 = 420 students

Degrees to Value

Value = (Degrees ÷ 360) × Total

Example: A slice of 72° in a pie chart with a total of £45,000.

Value = (72 ÷ 360) × 45,000 = 0.2 × 45,000 = £9,000

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Common Question Types

Type 1: Find the Value of a Segment

Given: Percentage (or degrees) of each segment, and the total.

Method: Multiply the percentage by the total.

Example: A pie chart shows expenditure categories. "Rent" is 28% of total expenditure of £3,500.

Rent = 28% × £3,500 = 0.28 × 3,500

• 25% of 3,500 = 875
• 3% of 3,500 = 105
• 28% = 875 + 105 = £980

Type 2: Find the Percentage of a Segment

Given: The value of a segment and the total.

Method: (Value ÷ Total) × 100

Example: A company's total revenue is £240,000. The "Services" segment represents £84,000.

Percentage = (84,000 ÷ 240,000) × 100 = 35%

Simplify: 84/240 = 7/20 = 35%

Type 3: Find the Total from a Segment

Given: The value and percentage of one segment.

Method: Total = Value ÷ (Percentage ÷ 100)

Example: The "Transport" segment represents 15% and is worth £2,700.

Total = 2,700 ÷ 0.15 = £18,000

Type 4: Compare Two Segments

Example: "How much more is spent on Food than on Clothing?"

Find the value of each segment and subtract.

Type 5: Combined Segments

Example: "What percentage is Food and Drink combined?"

Add the percentages (or degrees) of both segments.

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