Find the mean of the following frequency distribution using step - deviation method.


Class



0 - 10



10 - 20



20 - 30



30 - 40



40 - 50



Frequency



7



10



15



8



10


We will find the mean of the frequency distribution using step - deviation method, where A = Assumed mean and h = length of class interval.

Here, let A = 25 and h = 10


CLASS



MID - POINT(xi)



DEVIATION(di)


di = xi – 25



FREQUENCY(fi)



ui = di/h



fiui



0 - 10



5



- 20



7



- 2



- 14



10 - 20



15



- 10



10



- 1



- 10



20 - 30



25 = A



0



15



0



0



30 - 40



35



10



8



1



8



40 - 50



45



20



10



2



20



TOTAL





50




4



We have got


A = 25, h = 10, Σfi = 50 & Σfiui = 4


mean is given by





Thus, mean is 25.8


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