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

Find the mean and variance for the first $n$ natural numbers.

The standard deviation of the data $6, 7, 8, 9, 10$ is

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?

If each observation of a raw data whose variance is $\sigma^2$ is multiplied by $\lambda$,then the variance of the new set is

For a frequency distribution,the standard deviation is computed by: