Find the mean of the following data using step - deviation method:


Class



500 - 520



520 - 540



540 - 560



560 - 580



580 - 600



600 - 620



Frequency



14



9



5



4



3



5


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 = 550 and h = 20


CLASS



MID - POINT(xi)



DEVIATION(di)


di = xi – 550



FREQUENCY(fi)



ui = di/h



fiui



500 - 520



510



- 40



14



- 2



- 28



520 - 540



530



- 20



9



- 1



- 9



540 - 560



550 = A



0



5



0



0



560 - 580



570



20



4



1



4



580 - 600



590



40



3



2



6



600 - 620



610



60



5



3



15



TOTAL





40




- 12



We have got


A = 550, h = 20, Σfi = 40 & Σfiui = - 12


mean is given by





Thus, mean is 544.


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