# The Mean of the Following Distribution is 18. Find the Frequency F Of Class 19 – 21. - Mathematics

The mean of the following distribution is 18. Find the frequency f of class 19 – 21.

 Class 11-13 13-15 15-17 17-19 19-21 21-23 23-25 Frequency 3 6 9 13 f 5 4

#### Solution

 Class Frequency fi Mid value xi f_ix_i 11-13 3 12 36 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

Mean = (sumf_ix_i)/(sum f_i) = (704 + 20f)/(40 + f) = 18

=> 704 + 20f = 720 + 18f

=> 2f = 16

=> f = 8

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