Mean for Grouped data
Continuous series: The procedure of finding the arithmetic mean in this series, is the same as we have used in the discrete series. The only difference is that in this series, we are given class-intervals, whose mid-values (class-marks) are to be calculated first.
Formula, Arithmetic mean 
where x = mid-value
Example The weights (in gms) of 30 articles are given below :
14, 16, 16, 14, 22, 13, 15, 24, 23, 14, 20, 17, 21, 18, 18, 19, 20, 17, 16, 15, 11, 22, 21, 20, 17, 18, 19, 22, 23.
Form a grouped frequency table, by dividing the variate range into intervals of equal width, one class being 11-13 and then compute the arithmetic mean.
Solution:
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