Find the mean of the following frequency distribution, using the Assumed - mean method:


Class



100 - 120



120 - 140



140 - 160



160 - 180



180 - 200



Frequency



10



20



30



15



5


We will find the mean of the frequency distribution using Assumed - mean method, where A = Assumed mean.


CLASS



MID - POINT(xi)



FREQUENCY(fi)



DEVIATION(di)


di = xi – 150



fidi



100 - 120



110



10



- 40



- 400



120 - 140



130



20



- 20



- 400



140 - 160



150 = A



30



0



0



160 - 180



170



15



20



300



180 - 200



190



5



40



200



TOTAL




80




- 300



We have got


A = 150, Σfi = 80 & Σfidi = - 300


∵ mean is given by



⇒


⇒


Thus, mean is 146.25.


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