Circle Graphs / Pie Charts/ Pie Graphs

A pie chart (also called a Pie Graph or Circle Graph) makes use of sectors in a circle. The angle of a sector is proportional to the frequency of the data.

The formula to determine the angle of a sector is:

Constructing Circle Graphs

Study the following steps of constructing a circle graph:

Step 1 : Calculate the angle of each sector, using the formula

Step 2 : Draw a circle using a pair of compasses

Step 3 : Use a protractor to draw the angle for each sector.

Step 4 : Label the circle graph and all its sectors.

Example:

In a school, there are 750 students in Year1, 420 students in Year 2 and 630 students in Year 3. Draw a circle graph to represent the numbers of students in these groups.

Solution:

Total number of students = 750 + 420 + 630 = 1,800.

Draw the circle, measure in each sector. Label each sector and the pie chart.

Using Circle Graphs

We could also use a given circle graph to answer some questions about the data.

Example:

The following pie chart shows a survey of the numbers of cars, buses and motorcycles that passes a particular junction. There were 150 buses in the survey.

a) What fraction of the vehicles were motorcycles?

b) What percentage of vehicles passing by the junction were cars?

c) Calculate the total number of vehicles in the survey.

d) How many cars were in the survey?

Solution:

a) Fraction of motorcycles

b) To convert the angle of a sector into a percentage, we use the formula:

Percentage

Percentage of cars

c) Let x be the total number of vehicles

The total number of vehicles is 1,800

d) Number of cars

The following video shows how to answer questions based on given circle graphs.

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