1.

Find the mean of each of the following frequency distributions: Class interval: 0 - 6 6 - 12 12 - 18 18 - 24 24 - 30 Frequency: 7 5 10  12  6

Answer»

Let the assumed mean (A) = 15

 Class interval Mid value (xi) di = xi - 15 ui\(\frac{xi-15}{6}\) Frequency (fi) fiui
 3 - 6 3-12-27-14
 6 - 12  9-6-15-5
 12 - 181500100
 18 - 2421611212
 24 - 3027122612
 N = 40\(\sum\)fiui = 5

We have, 

A = 15

h = 6

Mean = A + h x \(\frac{\sum f_iu_i}{N}\)

= 15 + 6 x \(\frac{5}{40}\)

= 15 + 0.75 = 15.75



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