Find the variance of the first $20$ natural numbers.

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

$A$ student scores the following marks in five tests: $54, 45, 41, 43, 57$. His score is not known for the sixth test. If the mean score is $48$ in six tests,then the standard deviation of marks in six tests is

Consider the following frequency distribution:

$C$.$I$.	$75$-$175$	$175$-$275$	$275$-$375$	$375$-$475$	$475$-$575$	$575$-$675$	$675$-$775$
$f_i$	$3$	$2$	$1$	$0$	$1$	$2$	$3$

If the variance of this distribution is $60000$,then the coefficient of variation of the distribution is:

The variance of the following frequency distribution is:

Classes	$0-10$	$10-20$	$20-30$	$30-40$	$40-50$	$50-60$
Frequency	$11$	$29$	$18$	$4$	$5$	$3$

If $A$ and $B$ are the variances of the first $n$ even numbers and the first $n$ odd numbers respectively,then: