how do you find cumilative frequency for discrete frequency distribution?

Cumulative frequency is used to determine the number of observations that lie above (or below) a particular value in a data set. The cumulative frequency is calculated using a frequency distribution table, which can be constructed from stem and leaf plots or directly from the data.

Once you have decided that a stem and leaf plot is the best way to show your data, draw it as follows:

• On the left hand side of the page, write down the thousands, hundreds or tens (all digits but the last one). These will be your stems.
• Draw a line to the right of these stems.
• On the other side of the line, write down the ones (the last digit of a number). These will be your leaves.

For example, if the observed value is 25, then the stem is 2 and the leaf is the 5. If the observed value is 369, then the stem is 36 and the leaf is 9.
Suppose we have certain values given
31, 49, 19, 62, 24, 45, 23, 51, 55, 60, 40, 35 54, 26, 57, 37, 43, 65, 18, 41, 50, 56, 4, 54, 39, 52, 35, 51, 63, 42.
Then stem leaf and cumulative frequency is drawn as. E.g we write 4 as 04 in this 0 is stem and 4 is leaf .similarly in 18 1 is stem and 8 is leaf, in 19 also 1 is stem and 9 is leaf, so in stem 1 frequency is 2. Now cumulative frequency for stem 0 is 1 and for stem 1 Cumulative freq will be freq of stem 1 and Cumulative freq of stem 0, we will continue in same fashion.
 

Stem	Leaf	Frequency (f)		Cumulative frequency
0	4	1		1
1	8 9	2		1 + 2 = 3
2	3 4 6	3		3 + 3 = 6
3	1 5 5 7 9	5		6 + 5 = 11
4	0 1 2 3 5 9	6		11 + 6 = 17
5	0 1 1 2 4 4 5 6 7	9		17 + 9 = 26
6	0 2 3 5	4		26 + 4 = 30