Thirty women were examined in a hospital by a doctor and the number of heart beats per minute recorded and summarized as follows. Find the mean heart beats per minute for these women, choosing a suitable method.


Number of heart beats per minute:



65-68



68-71



71-74



74-77



77-80



80-83



83-86



Number of women:



2



4



3



8



7



4



2



Find the mean of each of the following frequency distributions: (5-14)

We may find class mark of each interval (xi) by using the relation.

xi =


Class size of this data = 3


Now taking 75.5 as assumed mean (A), we may calculate di, ui, fiui as following:


No. of heart beat per minute



Number of women (fi)



xi



di = xi – 75.5



ui =



fiui



65 – 68



2



66.5



-9



-3



-6



68 – 71



4



69.5



-6



-2



-8



71 – 74



3



72.5



-3



-1



-3



74 – 77



8



75.5



0



0



0



77 – 80



7



78.5



3



1



7



80 – 83



4



81.5



6



2



8



83 – 86



2



84.5



9



3



6




N = 30






fiui = 4



Now we may observe from table that fi = 30, fiui = 4


Mean (X̅) = di + * h


= 75.5 + * 3


= 75.5 + 0.4 = 75.9


So mean of heart beat per minute of women are 75.9 beats per minute.


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