The variance of $10$ observations is $16$. If each observation is doubled,then the standard deviation of the new data will be -

The mean of two samples of size $200$ and $300$ were found to be $25$ and $10$ respectively. Their standard deviations $(S.D.)$ are $3$ and $4$ respectively. Then,the variance of the combined sample of size $500$ is:

Students of two sections $A$ and $B$ of a class show the following results in a test conducted for $100$ marks. Then

	Section $A$	Section $B$
Number of students	$50$	$60$
Average marks in the test	$45$	$45$
Variance of distribution of marks	$64$	$81$

Find the variance of the first $n$ natural numbers.

The variance of the first ten multiples of $3$ is

Find the variance of the following discrete frequency distribution:

Class Interval	$0-2$	$2-4$	$4-6$	$6-8$	$8-10$
Frequency $(f_i)$	$2$	$3$	$5$	$3$	$2$