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Cumulative frequency is derived by adding the frequency distribution of a class interval and the frequencies of the earlier intervals upto that class interval. This is explained by an example below.

The following frequency distribution table shows the marks obtained by 40 students:

Table (a)

The frequencies may be added as indicated by the arrows, to get the cumulative frequency.

In the table(a), it is concluded that 4 students got marks 'less than 10', 9 students got marks 'less than 20' and so on.

The way it is distributed is called 'less than' cumulative frequency distribution.
Table (a) can be re-written as table (b).

Table (b)

In the same way 'Greater than' cumulative frequency distribution can be obtained by adding to the other frequencies in the reverse order also Solve Math Problems here.