Page 186 - Mathematics Coursebook

19.2 Interpreting and drawing pie charts

19.2 Interpreting and drawing pie charts

You can use a pie chart to display data showing how an amount is divided or shared. A pie chart is
drawn as a circle divided into sections called sectors. # e angles at the centres of all the sectors add up
to 360°. When you draw a pie chart you must make sure that you label each sector and draw the angles
accurately.

Worked example 19.2
Favourite animals of the
a The pie chart shows the favourite animal of the students in class 7A
students in class 7A.
i Which animal is the most popular?
ii Which animal is the least popular? Donkey
iii Can you tell from the pie chart how many students Dog
are in class 7A? Horse
b The table shows the favourite animal of the students Animal Frequency
in class 7B. Cat
Draw a pie chart to show this information. dog 8
cat 7
horse 10
donkey 5

a i Dog is the most popular. Dog has the biggest sector of the pie chart.
ii Cat is the least popular. Cat has the smallest sector of the pie chart.
iii No The pie chart only shows the fraction, or proportion, of the students
who like the various animals, not the actual numbers.
b 8 + 7 + 10 + 5 = 30 First add the frequencies to work out the total number of students in
360° ÷ 30 = 12° the class. Work out the number of degrees per student by dividing the
Dog: 8 × 12 = 96° total number of students into 360°. Multiply each frequency by 12° to
Cat: 7 × 12 = 84° get the total number of degrees for each sector.
Horse: 10 × 12 = 120° Check that the total of the degrees does add up to 360°.
Donkey: 5 × 12 = 60° 96° + 84° + 120° + 60° = 360°
Start by drawing a circle and then draw a line from the centre to the
Favourite animals of the
students in class 7B top of the circle. Measure an angle of 96° for the ‘dog’ sector, then
draw a straight line from the centre to the edge of the circle. Repeat
for the other sectors. Label each sector with the name of the animal
Donkey and give the chart a title.
Dog

Horse
Cat

) Exercise 19.2 Favourite colour

1 The pie chart shows the favourite colours chosen by 40 people. Red
a Which colour is the most popular?
b Which colour is the least popular? Green Yellow
c Explain how you can tell from the pie chart that blue is the Blue
favourite colour of 10 of the people.

19 Interpreting and discussing results 185