Page 181 - MAT KS3 Y8 Cambridge CheckPoint

18.1 Interpreting and drawing frequency diagrams

18.1 Interpreting and drawing frequency diagrams

Frequency diagrams show how often particular values occur in a set of data. One example of a
frequency diagram is a bar chart. In bar charts, bars can be used to represent frequency.

When you draw a bar chart for discrete data When you draw a bar chart for continuous data
you should make sure that: you should make sure that:
r the bars are all the same width r the bars are all the same width
r there is equal gap between the bars r there are no gaps between the bars
r you write the data groups under each bar r you use a sensible scale on the horizontal axis
r you give the frequency diagram a title and r you give the frequency diagram a title and
label the axes label the axes
r you use a sensible scale on the vertical axis. r you use a sensible scale on the vertical axis.

Worked example 18.1
Number of pieces of fruit eaten by 8T in one week
a The frequency diagram shows how many pieces of fruit
the students in class 8T ate in one week. 10
i How many students ate 4–7 pieces of fruit?
ii How many more students ate 8–11 pieces of fruit than 8
12–15 pieces?
iii How many students are there in class 8T? 6
b The frequency table shows the masses of 20 teachers, Frequency
measured to the nearest kilogram.
Draw a frequency diagram to show the data. 4
Mass, m (kg) Frequency
60 < m ⩽ 70 3 2
70 < m ⩽ 80 8
0
80 < m ⩽ 90 6 0 –3 4–7 8–11 12–15
90 < m ⩽ 100 4 Number of pieces of fruit

a i 6 students The bar for 4–7 has a height of 6 on the frequency axis.
ii 9 − 4 = 5 students The frequency for 8–11 is 9 and the frequency for 12–15 is 4.
Subtract one from the other to find the difference.
iii 7 + 6 + 9 + 4 Add together the frequencies for all the groups.
= 26 students
b The bars are all the same width and, as the data is
Mass of 20 teachers
continuous, there are no gaps between them.
8 The horizontal and vertical axes both have a sensible
scale.
The frequency diagram has a title and the axes are
Frequency 6 labelled.

4

2

0
50 60 70 80 90 100 110
Mass (kg)

18 Interpreting and discussing results 179