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Pioneers Maths

Maths · Statistics & Probability

Pie charts & scatter graphs

Read and construct pie charts and scatter graphs.

Not startedCAMBRIDGE · 8CBSE · VIIIIB · MYP-2

What is a pie chart?

A pie chart is a circular graph that shows data as slices. Each slice represents a category. The bigger the slice, the larger that category's share. The whole circle always represents 100% of the data. Pie charts help us compare parts of a whole at a glance.

Angles in pie charts

A full circle has 360 degrees. To find the angle for each slice, work out what fraction of the total it represents. Then multiply that fraction by 360. For example, if one category is a quarter of the data, its angle is 90 degrees.

What is a scatter graph?

A scatter graph (or scatter diagram) plots pairs of values as points on a grid. It shows whether two variables are related. If the points form a pattern, there may be a correlation (relationship). A line of best fit can help show trends in the data.

Reading scatter graphs

Each point shows two linked values, one on each axis. For example, height and shoe size. If points slope upwards, both variables increase together (positive correlation). If points slope downwards, one increases while the other decreases (negative correlation). Scattered points mean no clear relationship.

Constructing graphs

For pie charts, calculate each angle and draw slices using a protractor. Label each slice clearly. For scatter graphs, plot each pair of values as a single point. Use a ruler to draw a line of best fit if there is a trend. Always label both axes with units.

Worked examples

  1. 1. A class survey shows 12 students like football, 8 like tennis and 4 like swimming. Find the angle for football in a pie chart.

    1. Total number of students: 12 + 8 + 4 = 24
    2. Fraction who like football: 12/24 = 1/2
    3. Angle for football: 1/2 × 360 = 180 degrees

  2. 2. In a pie chart, the slice for cats has an angle of 120 degrees. What percentage of the total does this represent?

    1. A full circle is 360 degrees, which represents 100%
    2. Fraction of circle: 120/360 = 1/3
    3. Convert to percentage: 1/3 × 100 = 33.3% (approximately)

  3. 3. A scatter graph shows points at (2, 5), (4, 9), (6, 13). Is there a correlation?

    1. Check if there is a pattern: as the first value increases, so does the second
    2. The points form an upward sloping pattern
    3. This shows a positive correlation between the two variables

Try it yourself

A pie chart shows favourite fruits. Apples have an angle of 90 degrees. What fraction of people chose apples?

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