Question

Find the missing frequency (p) for the following distribution whose mean is 7.68.

x:	3	5	7	9	11	13
f:	6	8	15	p	8	4

Answer 1

\(Mean =\frac{ \sum fx}{N}\)

= \(\frac{(9p\, +\, 303)}{(p\,+\,41)}\) 

Mean = 7.68 

So, \(\frac{(9p\, +\, 303)}{(p\,+\,41)}\) = 7.68 

9p + 303 = 7.68 (p + 41) 

9p + 303 = 7.68p + 314.88 

9p − 7.68p = 314.88 − 303 

1.32p = 11.88 

or p = \(\frac{(11.881)}{(1.32)}\) 

= 9 

⇒ The value of p is 9.