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

x
f
fx
3
6
18
5
8
40
7
15
105
9
P
9p
11
8
88
13
4
52
 
N = p + 41
$\sum\text{fx}=\text{9p}+303$

It is given that,

Mean = 7.68

$\Rightarrow\frac{\sum\text{fx}}{\text{N}}=7.68$

⇒ 9p + 303p + 41 = 7.68

⇒ 9p + 303 = 7.68p + 314.88

⇒ 9p − 7.68p = 314.88 - 303

⇒ 1.32p = 11.88

⇒ p = 11.881.32 = 9

⇒ p = 9

$\therefore$ P = 9

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