In a pie chart it is important to understand that the angle of each sector represents the fraction, out of , assigned to that data value. Pie charts should always be labelled, either directly on the pie chart or by means of a colour-coded key.
This pie chart shows the results of a survey to find out how students travel to school:
a) What is the most common method of travel?
b) What fraction of the students travel to school by car?
c) If students travel by car, how many people took part in the survey?
a) The most common method of travel is bus as this has the largest sector on the pie chart.
b) of the students travel by car because the angle of the sector is , and the fraction is .
c) students travel by car, and this is of the total. Therefore, people were questioned for the survey.
A supermarket chain sold packets of sausages last month.
The pie chart below shows the different varieties:
a) How many packets of vegetarian sausages were sold?
b) How many packets of beef sausages were sold?
a) Vegetarian sausages account for of the total sales, so calculate of .
. Therefore, packets of vegetarian sausages were sold last month.
b) There are in a complete turn.
The 'beef' sector has an angle of , so the beef sector is of the circle. . Therefore, packets of beef sausages were sold.