Using an appropriate method, find the mean of the following frequency distribution:


Class interval



84 - 90



90 - 96



96 - 102



102 - 108



108 - 114



114 - 120



Frequency



8



10



16



23



12



11




Which method did you use, and why?

For equal class intervals, we will solve by finding mid points of these classes using direct method.


CLASS



MID - POINT(xi)



FREQUENCY(fi)



fixi



84 - 90



87



8



696



90 - 96



93



10



930



96 - 102



99



16



1584



102 - 108



105



23



2415



108 - 114



111



12



1332



114 - 120



117



11



1287



TOTAL




80



8244



We have got


Σfi = 80 & Σfixi = 8244


∵ mean is given by



⇒


⇒


Thus, mean is 103.05


Here, the method being used is direct method as it is easy to calculate the mid - points of the class intervals and the rest calculations were simple and easy.


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