# Cumulative frequency

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- Created by: Bhavik
- Created on: 05-06-11 16:06

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Cumulative frequency diagrams

The cumulative frequency is obtained by adding up the frequencies as you go along to give a

'running total'.

Drawing a cumulative frequency diagram

The table shows the lengths (in cm) of 32 cucumbers.

Before drawing the cumulative frequency diagram, we need to work out the cumulative

frequencies. This is done by adding the frequencies in turn.

Length Frequency Cumulative Frequency

21 24 3 3

25 28 7 10 (= 3 + 7)

29 32 12 22 (= 3 + 7 + 12)

33 36 6 28 (= 3 + 7 + 12 + 6)

37 40 4 32 (= 3 + 7 + 12 + 6 + 4)

The points are plotted at the upper class boundary. In this example the upper class

boundaries are 24.5, 28.5, 32.5, 36.5 and 40.5. Cumulative frequency is plotted on the

vertical axis.

There are no values below 20.5cm.

Remember, cumulative frequency graphs are always plotted using the highest value in each

group of data and the cumulative frequency is always plotted up a graph, never across.

The cumulative frequency diagram always has this characteristic Sshape.

Finding the median and quartiles

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