Rukasha Maths

GCSE maths Beta

Charts, tables and scatter graphs · Revision guide

Foundation · Statistics · 1 page in the PDF

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Learning objectives

  • Read chart scales and calculate pie-chart angles.
  • Describe correlation and judge predictions from scatter graphs.

Key ideas

Read the title, labels, scales and key before interpreting a chart.

Pie-chart angles show each category as a fraction of the total.

sector angle=category frequencytotal frequency×360∘\text{sector angle}=\frac{\text{category frequency}}{\text{total frequency}}\times360^\circ

Scatter graphs plot paired values; do not join individual points with a zigzag line.

Positive correlation trends upwards; negative correlation trends downwards. Correlation does not establish cause.

Interpolation predicts within the observed range. Extrapolation predicts outside it and may be unreliable.

Worked examples

Example 1

Fifteen of forty students choose cycling. Find the cycling sector angle.

cycling fraction=1540\text{cycling fraction}=\frac{15}{40}
sector angle=1540×360∘=135∘\text{sector angle}=\frac{15}{40}\times360^\circ=135^\circ
135∘135^\circ

Example 2

One pictogram symbol represents eight pupils. Interpret two and a half symbols.

2.5×8=20 pupils2.5\times8=20\text{ pupils}
20 pupils20\text{ pupils}

Watch out

A trend does not prove cause and effect. Predictions beyond the observed values deserve extra caution.