Reading and interpreting pie charts

Reading and interpreting pie charts

We can read and draw pie charts in order to obtain the required information.

When reading and drawing pie charts, relate the number of items with the total degrees of a circle. For example, study the following pie chart which represent the expenditure of Farida's monthly salary:

Expenditure of Farida's monthly salary.

The graph shows that a large fraction of Farida's salary is used for food.

The rest is used for tax, transport fare and communication.

In pie charts, angles represent the number of objects. The largest number of objects are represented by the largest angle and the smallest number of objects are represented by the smallest angle.

Note that, the decimal solution for questions involving people, animals or things are approximated to a whole number.

Example 1

The following pie chart shows the distribution of households in some villages in Njombe district for the year 2005:

If the total number of households in Kipengele, Makoga and Igosi villages is 24,000, answer the following questions:

(a) Which village has the largest number of households?

(b) Which village has the smallest number of households?

(c) What fraction represent the households in Kipengele village?

Solution

(a) The village with the largest number of households is the one represented by the largest angle. Therefore, Makoga village has the largest number of households.

(b) The village with the smallest number of households is the one represented by the smallest angle. Therefore, Igosi has the smallest number of households.

(c) The fraction representing the number of households in Kipengele village is 123/360 or 41/120 of all households.

Example 2

The following pie chart shows the proportion of people in Mbeya town in the year 2007.

If Mbeya town had 900,000 people in that year, answer the following questions:

(a) How many children were there?

(b) How many men were there?

(c) How many women were there?

(d) Which category of people had the largest number of people?

(e) What fraction of all the people were men?

Solution

The number of people for each group is found by using the size of the representative angle in the pie chart.

Therefore,

Number of people = Size of the angle/Sum of angles in a circle × total number of people

(a) Number of children = 123°/360° × 900,000 = 307,500

Therefore, the number of children is 307,500.

(b) Number of men = 113°/360° × 900,000 = 282,500

Therefore, the number of men is 282,500.

(c) Number of women = 124°/360° × 900,000 = 310,000

Therefore, the number of women is 310,000.

(d) Women were more than men and children.

(e) Men were 113/360 of all the people.