1. How to draw a cumulative frequency graph

2. If the data is jumbled, sort it out by using a table
23, 24, 34, 45, 56, 23, 57, 41, 37, 65, 17, 26, 35, 44, 33, 48, 19, 61, 58, 55, 49, 44, 57, 43
Data
Frequency
10 – 20 2
20 – 30 4
30 – 40 5
40 – 50 7
50 – 60
60 – 70
You must decide sensible intervals

3. Complete the third column by adding the second column like this:
Data
Frequency
Cumulative Frequency
10 – 20 2
20 – 30 4
2 + 4 = 6
30 – 40 5
= 11
40 – 50 7
= 18
50 – 60
= 22
60 – 70
= 24

4. You don’t have to show working
Data
Frequency
Cumulative Frequency
10 – 20 2
20 – 30 4 6
30 – 40 5 11
40 – 50 7 18
50 – 60 22
60 – 70 24

5. Plot the second number in the data column against the number in the cumulative frequency column
10 – 20 2
20 – 30 4 6
30 – 40 5 11
40 – 50 7 18
50 – 60 22
60 – 70 24
Plot these numbers

6. Now, join up the points

7. You can use this to find the middle half
¾ (18)
(12)
Upper Q
(53)
(6)
Lower Q
(30)
Median
(42)

8. The Lower Quartile is 30 Median is 42 The Upper Quartile is 53
This means that the middle half is between 30 and 53. Called the inter-quartile range. 53 – 30 = 23
The Lower Quartile is 30
Median is 42
The Upper Quartile is 53