The following table gives the number of children of 150 families in a village

No. of children ($x$):	0	1	2	3	4	5
No. of families ($f$):	10	21	55	42	15	7

Find the average number of children per family.

Given:

The number of children of 150 families in a village.

To do:

We have to find the average number  of children per family.

Solution:

Let the assumed mean be $A=3$

Number of children ($x_i$)	Number of families ($f_i$)	$d_i = x_i -A$  $A =3$	$f_i \times\ d_i$
0	10	$-3$	$-30$
1	21	$-2$	$-42$
2	55	$-1$	$-55$
3 - $A$	42	0	0
4	15	1	15
5	7	2	14
Total	$\sum{f_i}=150$		$\sum{f_id_i}=-98$

 We know that,

Mean $=A+\frac{\sum{f_id_i}}{\sum{f_i}}$ 

Therefore,

Mean $=3+\frac{-98}{150}$

$=3-0.65$

$=2.35$

The number of children per family is $2.35$.