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= 16.307
Therefore, average cost = 16.307

METHOD OF CALCULATING MEAN OF GROUPED DATA

To calculate the mean of grouped data, we have following three methods:

(1)Direct Method

(2)Assumed Mean Method

(3)Step Deviation Method

3-Step Deviation Method-

Step deviation method is used in the cases, where the deviation from the assumed
mean are multiples of a common numbers. If the values of di for each class is a
multiple of h(class size=U.L – L.L),the calculation becomes simpler by using ui=
di  xi  A
h h

 fiui xi  A
The Arithmetic Mean = x = A x h where ui =
 fi h

Note:

1)If the class sizes are not equal for each class interval, then we take h to be a suitable
divisor of all the di’s.

2)The mean obtained by all the three methods is always the same.

3)The assumed mean method and step deviation method are just simplified forms of
the direct method.

4)If the given data is discontinuous, there is no need to convert it into continuous data,
while finding the mean. Because mid value xi of each class interval would be same
either class interval is continuous or not continuous.

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