Pie charts are based on fractions of 360°.

The fractions can be worked out from the angles at the centre of the chart.

This pie chart shows the results of a survey on favourite crisp flavours.

The Salt and Vinegar sector shows 36° which is 36/360 of the whole circle (i.e. 1/10)

Now we need a hard fact, such as the actual number who chose Salt and Vinegar or the total number in the survey.

Example 1

If 15 people chose Salt and Vinegar, how many people took part in the survey?

Answer

15 people are shown in 1/10 of the circle, so there must be 10 x 15 = 150 people in total.

Example 2

If 40 people took the survey, how many people chose Salt and Vinegar?

Answer

We need to work out 1/10 of 40 = 4, so 4 people chose Salt and Vinegar.