year 8 maths

9D
Sector graphs and divided bar graphs
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9D Sector graphs and divided bar graphs
A sector graph (also called a pie chart) consists of a circle divided into different sectors or ‘slices of pie’,
where the size of each sector indicates the proportion occupied by any given item. A divided bar graph
is a rectangle divided into different rectangles or ‘bars’, where the size of each rectangle indicates the
proportion of each item. Both types of graphs are suitable for categorical but not numerical data.
If a student is asked to describe how much time they spend each evening doing different activities, they
could present their results as either type of graph:
internet
homework
sport
sport
TV
homeworkinternet
TV
0% 20% 40% 60% 80% 100%
sport TV homework internet
From both graphs, it is easy to see that most of the student’s time is spent playing sport and the least
amount of time is spent using the internet.
Let’s start: Student hobbies
Rania, Kristina and Ralph are asked to record how they spend their time after school. They draw the
following graphs.
Rania
Kristina
Ralph
internet
homework
TV
homework
homework
internet
TV
sport
sport
• Based on these graphs alone, describe each student in a few sentences.
• Justify your descriptions based on the graphs.
■ To calculate the size of each section of the graph, divide the value in a given category by the
sum of all category values. This gives the category’s proportion or fraction.
■ To draw a sector graph (also called a pie chart ), multiply each category’s proportion or
fraction by 360° and draw a sector of that size.
■ To draw a divided bar graph , multiply each category’s proportion or fraction by the total
width of the rectangle and draw a rectangle of that size.
Key ideas
Cambridge Maths NSW
Stage 4 Year 8 Second edition
ISBN 978-1-108-46627-1 © Palmer et al. 2018
Cambridge University Press
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