1. Mathematics
Pie Charts

2. Lesson Objectives The aim of this powerpoint is to help you…
to learn how to draw and interpret a pie chart.

3. Pie Charts - Interpreting
Unless you have the original data, you can not tell how many items are included in each section.
You can only see what proportion (fraction or percentage) of the total of items falls into each category.
The bigger the sector (i.e. angle at the centre) of the pie chart, the bigger the proportion of items in that category.

4. Pie Charts – Interpreting (cont’d)
The proportion (as a fraction) of each category is EITHER that category’s frequency over the total frequency OR that category’s angle over (You may be asked to give your answer in its simplest form so you will need to cancel the fraction down).
To calculate the rate of ‘degrees per item’ EITHER divide 360 by the total frequency OR one sector’s angle by it’s frequency.
To calculate the number of items for each category, divide that category’s angle by this rate.

5. Interpreting Pie Charts - Example
Maddie undertakes a survey of how the students in her class get to school. She represents these results in a pie chart…
24°
108° 48°
180°

6. Interpreting Pie Charts - Example
Q1. What was the most
common mode of
transport?
Ans. The biggest sector belongs to Car
Q2. What fraction of the class travel by bus?
Ans. 48° out of the whole 360° = = 1
24°
108° 48°
180°

7. Interpreting Pie Charts - Example
If 9 people walk…
Q3. How many people
are there in her
class altogether?
Ans. 9 people = 108°
so 108° ÷ 9 = 12° per person
The whole pie chart = 360°
This equates to 360° ÷ 12° = 30 people
24°
108° 48°
180°

8. Pie Charts - Drawing
The whole pie chart of 360° must be shared equally between the total number of items (i.e. total frequency) – this will give you a rate of the number of degrees per item (beware it might not be a whole number)
Multiply each category’s frequency by this rate to calculate the angle needed for its sector.
Using a set of compasses draw a circle.

9. Pie Charts - Drawing
Draw a vertical line from the centre to the top and measure the first category’s angle, and draw its other line.
Measure the next category’s angle from this new line and so on.
At the end, label each sector individually with the name of its category. It is also useful to write the angle value of each sector at the centre.

10. Drawing Pie Charts - Example
Tony observes the eye colour of the students in his class. His results are in the table below.
Draw a pie chart to represent this data.
Eye Colour
No. of Students
Blue 8
Brown 11
Green 5

11. Drawing Pie Charts - Example
The total number of students = = 24
Share the pie chart equally between these students
360° ÷ 24 = 15° per student
Multiply each category’s frequency (i.e. number of students) by this rate.
CHECK: Total angle = 360° ( = 360 P)
Eye Colour
No. of Students
Blue 8
Brown 11
Green 5
Angle
x 15 = 120°
x 15 = 165°
x 15 = °

12. Drawing Pie Charts - Example
Draw a circle.
Eye Colour
No. of Students
Angle (°)
Blue 8
120
Brown 11
165
Green 5 75
Now label each sector
It’s good practice to put in the angles too.
Most people like to colour in their pie chart.
Measure the second angle and draw it’s other line.
Check: Measure the remaining angle it should be 75°
Draw a line from the centre to the top.
Measure the first angle and draw it’s other line.
Green
Blue
Brown
75°
120°
165°

13. What next? Print out and read through the notes called Data9.
Work through the MyMaths lesson and then its online homework task called Drawing Pie Charts which can be found at:
Lesson:
Online HW:
Work through the MyMaths lesson and then its online homework task called Reading Pie Charts which can be found at:
Lesson:
Online HW:
Answer the tasks that appear throughout the Data9 notes.
Work through the MyMaths lesson and its online homework task called Misleading Graphs which can be found at:
Lesson:
Online HW:
Now move on to the Data-10 powerpoint