Question 3:

The following distribution shows the daily pocket allowance of children of a locality.
The mean pocket allowance is Rs.18. Find the missing frequency f.

Answer:

To find the class mark (x_i) for each interval, the following relation is used.

Given that, mean pocket allowance, 

Taking 18 as assured mean (a), d_i and f_id_i are calculated as follows.

From the table, we obtain

Hence, the missing frequency, f, is 20.

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