What is a Pie Chart?

A pie chart is a circle divided into slices (sectors). Each slice represents a category of data. The size of each slice depends on the number or amount it represents. The whole circle represents the total, which equals 360 degrees.

Reading Information from a Pie Chart

When we read a pie chart, we look at the size of each angle:

• Larger angle = larger quantity
• Smaller angle = smaller quantity

The angle size tells us what fraction of the whole each category represents.

Calculating Values from a Pie Chart

To find the actual number represented by a sector, use this formula:

$Number\ of\ items = \frac{angle}{360°} \times total\ number\ of\ items$

Worked Example 1: Households in Villages

The pie chart below shows the distribution of households in three villages: Kipengele, Makoga, and Igosi.

If the total number of households in these three villages is 24,000, answer the following:

(a) Which village has the largest number of households?
(b) Which village has the smallest number of households?
(c) What fraction represents the households in Kipengele village?

Solutions

(a) The village with the largest angle has the most households. From the chart, Makoga has the largest angle, so it has the largest number of households.

(b) The village with the smallest angle has the fewest households. From the chart, Igosi has the smallest angle, so it has the smallest number of households.

(c) If the angle for Kipengele is 123°, then the fraction is:

$\frac{123°}{360°} = \frac{41}{120}$

So households in Kipengele represent 41/120 of the total.

Worked Example 2: Population of Mbeya Town

The pie chart shows the proportion of people in Mbeya town: children, men, and women.

If the total population is 900,000, find:

(a) How many children were there?
(b) How many men were there?
(c) How many women were there?

Solutions

(a) Children: angle = 123°

$Number = \frac{123°}{360°} \times 900,000 = 307,500$

There were 307,500 children.

(b) Men: angle = 113°

$Number = \frac{113°}{360°} \times 900,000 = 282,500$

There were 282,500 men.

(c) Women: angle = 124°

$Number = \frac{124°}{360°} \times 900,000 = 310,000$

There were 310,000 women.

Presenting Data in a Pie Chart

To present data in a pie chart:

1. Add all the values to get the total.
2. Find the angle for each category using:
   $Angle = \frac{category\ value}{total} \times 360°$
3. Draw a circle and divide it into sectors using the calculated angles.
4. Label each sector with its category name and value.

What is a Histogram?

A histogram is a statistical diagram that shows how data is distributed across continuous groups. Unlike bar charts, in a histogram the bars are joined together (no gaps between them) because the data is in groups called class intervals.

Reading a Histogram

When reading a histogram:

• The horizontal axis (x-axis) shows the class intervals.
• The height of each bar shows the frequency (how many items are in that group).
• Taller bar = more items in that group.
• Shorter bar = fewer items in that group.

Worked Example 3: Marks in a Class Test

The histogram below shows the marks scored by Standard VI pupils in a Mathematics test.

Answer these questions:

(a) How many pupils scored between 41 and 60 marks?
(b) What is the most common score range?
(c) How many pupils took the test?

Solutions

(a) The bar for interval 41-60 has height 12, so 12 pupils scored in this range.

(b) The tallest bar is for 41-60, so the most common score range is 41 to 60 marks.

(c) Total pupils = 5 + 8 + 12 + 10 + 5 = 40 pupils

Presenting Data in a Histogram

To present data in a histogram:

1. Organize data into class intervals (groups with equal width).
2. Count the frequency (number of items) in each interval.
3. Draw the horizontal axis with class intervals.
4. Draw the vertical axis with frequency.
5. Draw bars for each class interval with no gaps between them.
6. Label the axes and give the histogram a title.

• Pie charts show parts of a whole circle. Use angles to find values.
• Formula: $Number = \frac{angle}{360°} \times total$
• Histograms show frequency distribution with connected bars.
• In histograms, bars touch each other because data is continuous.
• Both diagrams help us compare and understand data quickly.

In Tanzania, pie charts and histograms are used in everyday life. For example, a shopkeeper in Dar es Salaam can use a pie chart to see which items (rice, sugar, cooking oil, or flour) sell most each month. A hospital can use a histogram to show how many patients visit the clinic each week, helping the staff plan their work. These diagrams help people make better decisions based on real information.