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How to Get the Cumulative Frequency?

TopCumulative Frequency is the current frequency which is sum of frequencies up to or including the current frequency value. This frequency can be time dependent or a space dependent. Cumulative frequency (FC) is also the frequency whose current value 'V' is less than or equal to the reference frequency value (Vr) i.e. F (V ≤ Vr).The relative cumulative frequency can be calculated as the frequency F(V ≤ Vr) or F (Vr) = Pvr / Nobs. Where Pvr is the number of values less than reference value Vr and Nobs is the number of total observations. Now question arises how to get cumulative frequency. Let us understand this with the help of small example.
Example::

In this Example we have three columns, in the first column we have marks obtained by the students from range 0 - 30, 30 - 60 and so on, we have another column of frequency i.e. 2, 6, 4, 8, 10, 12, 14, 16 and last third column is of calculation of cumulative frequency. The first value of Fc is 2 after that we have second value, that is Sum of 2 (Fc) and 6 (second value in Frequency column) is 8 that is the cumulative frequency (Fc). Similarly we have the second cumulative frequency as 16, which is sum of 8 (Second cumulative frequency) and 8(the third value of the frequency column).
Similarly we can calculate cumulative frequencies of all values in table from range of obtained marks 0 - 30 to 180 - 210.
Cumulative frequency is used for calculating reliability analysis. From reliability analysis it gives the total number of events occurred up to given values in analysis table.
The graph of cumulative frequency gives a proper description of the analysis made.