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  • If the mean of the following frequency distribution is 62·8, then find the missing frequency x : Class</str

If the mean of the following frequency distribution is 62·8, then find the missing frequency x :

Class 0-20 20-40 40-60 60-80 80-100 100-120
Frequency 5 8 x 12 7 8

 

 

 

 

 
 
 
 
 

Answers (1)

Class Frequency (f_i) x_i

f_ix_i
0-20 5 10 50
20-40 8 30 240
40-60 x 50 50x
60-80 12 70 840
80-100 7 90 630
100-120 8 110 880

\sum f_i = 40+x

\sum f_ix_i = 2640 + 50x

By direct method :

\text{Mean}=\frac{\sum f_ix_i}{\sum f_i}

62.8 =\frac{2640+50x}{40+x}

62.8(40+x) =2640+50x

2512 + 62.8 x =2640+50x

62.8 x - 50x = 2640-2512

12.8 x = 128

x = 10

Therefore, the missing frequency is 10.

Posted by

Ravindra Pindel

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