Find the mean of the following frequency distribution by a suitable method.

C.I.	50-70	70-90	90-110	110-130	130-150	150-170
Frequency	8	12	13	27	18	22

$\Rightarrow$ By using direct method we are going find mean :

$C.I$	$Frequency$ $f_i$	$Class-mark$ $x_i$	$f_i{x}_i$
$50-70$	$8$	$60$	$480$
$70-90$	$12$	$80$	$960$
$90-110$	$13$	$100$	$1300$
$110-130$	$27$	$120$	$3240$
$130-150$	$18$	$140$	$2520$
$150-170$	$22$	$160$	$3520$
	$\sum f_i=100$		$\sum f_i{x}_i=12020$

$\overline{x}=\frac{\sum f_i{x}_i}{\sum f_i}$

$=\frac{12020}{100}$

$=120.2$