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Circle Graph or Pie Chart

A circle graph or pie chart is another important pictorial Favourite Subject
representation of data that is used in the fields of business, Social science 10%
mass media, budgeting, etc. It is a type of graph representing Mathematics
data in a circular form, with each slice (called a sector) of the 40% English
20%
circle representing a fraction or proportionate part of the
whole. Since, the sectors resemble the slices of a pie, a circle
graph is also called a pie chart.
Science 25%
Thus, a circle graph shows the relationship between a whole Hindi 5%
and its parts and is generally used to compare the parts with the whole. The given circle graph
shows the favourite subjects of class VIII students in percentage.

Construction of a Circle Graph or Pie Chart

We know that the total number of degrees in the circular arc is 360°. Therefore, in drawing a
circle graph or pie chart, we first construct a circle and divide it into as many sectors as there are
components of the data. Each sector represents a different component of the data. This is obtained
by subdividing the total angle at the centre of the circle in specified proportions.

Thus, to construct a circle graph, proceed as follows:

1. Find the sum of various component values.
2. Calculate the central angle for each data value as

Value of the component
Central angle = × 360 °
Sum of the values of alll components

3. Draw a circle of any radius and divide it into sectors of appropriate size after calculating the
central angle for all components.

4. Start with a horizontal/vertical radius and keep moving in the clockwise direction.
5. Label and shade each sector.

Let us understand it with an example. Consider the time spent by a child during a day.
Sleep — 8 hours; School — 6 hours; Homework — 4 hours; Play — 4 hours; Others — 2 hours

To draw a pie chart of the data given, let us calculate the central angle as shown below.

Time spent in an activity
Activity Time Spent (in hours) Central angle = Total time in a day × × 360°

8
Sleep 8 × 360° = 120°
24
6
School 6 × 360° = 90°
24
4
Homework 4 × 360° = 60°
24

105 Data Handling