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


Daily pocket allowance (in Rs)



11 - 13



13 - 15



15 - 17



17 - 19



19 - 21



21 - 23



23 - 25



Number of children



7



6



9



13



f



5



4


The above given data can be represented in the form of table as below:


Class Interval



fi



xi



fixi



11-13



7



12



84



13-15



6



14



84



15-17



9



16



144



17-19



13



18



234



19-21



f



20



20f



21-23



5



22



110



23-25



4



24



96




∑fi = 44 + f




∑fixi = 752 + 20f



We can find the value of f as follows:



18


18( 44 + f ) = 752 + 20f


792 + 18f = 752 + 20f


2f = 40


F = 20


19