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

The mean and variance of $10$ observations were calculated as $15$ and $15$ respectively by a student who took by mistake $25$ instead of $15$ for one observation. Then,the correct standard deviation is $.....$

The standard deviation of the first $n$ natural numbers is . . . . . . .

The variance for the first six prime numbers greater than $5$ is

The variance of the first $10$ multiples of $3$ is: