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Question

# Can we use assumed mean method to find the mean of grouped data when its class interval are irregular.If not why?

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Solution

## When the class intervals are continuous but each of the given classes of unequal width, then we can find the mean with the help of any of the 3 methods : Direct method Assumed mean method Step deviation method Consider the following example. A class teacher has the following absentee record of 40 students of a class for the whole term. Find the mean number of days a student was absent. No. of days 0-6 6-10 10-14 14-20 20-28 28-38 38-40 No. of students 11 10 7 4 4 3 1 Here is the solution. CLASS INTERVAL FREQUENCY (fi) CLASS MARKS(xi) fixi 0-6 11 3 33 6-10 10 8 80 10-14 7 12 84 14-20 4 17 68 20-28 4 24 96 28-38 3 33 99 38-40 1 39 39 Total ∑ fi = 40 ∑ fi xi = 499 Mean = ∑ fi xi / ∑ fi = 499/40 = 12.475 ≈ 12.48 Note: Direct method should be used when the given data is small. Assumed mean method for intermediate data and for huge data we can use step deviation method.

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