The variance of $20$ observations is $5$. If each of the observations is multiplied by $2$,then the variance of the resulting observations is:

Find the variance of the following frequency distribution.

$Class$	$0-2$	$2-4$	$4-6$	$6-8$	$8-10$	$10-12$
$f_i$	$2$	$7$	$12$	$19$	$9$	$1$

Suppose a population $A$ has $100$ observations $101, 102, . . ., 200$ and another population $B$ has $100$ observations $151, 152, . . ., 250$. If $V_A$ and $V_B$ represent the variances of the two populations,respectively,then $V_A / V_B$ is:

The sum of squares of deviations for $10$ observations taken from mean $50$ is $250$. The coefficient of variation is.....$\%$

If the standard deviation of the numbers $2, 3, a$,and $11$ is $3.5$,then which of the following is true?

The mean and the standard deviation $(s.d.)$ of five observations are $9$ and $0,$ respectively. If one of the observations is changed such that the mean of the new set of five observations becomes $10,$ then their $s.d.$ is?