# how to find the mean if the class intervals are unequal??like fr e- 0-10,10-30,30-35....

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 $\approx$ 12.48

• 30

You can Use the Step-Deviation Method. Take a Suitable height (maybe 10).

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