If the variance of the terms in an increasing $A.P.$,$b_{1}, b_{2}, b_{3}, \ldots, b_{11}$ is $90$,then the common difference of this $A.P.$ is

Let $x_1, x_2, \dots, x_n$ be $n$ observations such that $\sum x_i^2 = 300$ and $\sum x_i = 60$. Which of the following is a possible value for $n$?

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

The sum of $100$ observations and the sum of their squares are $400$ and $2475$,respectively. Later on,three observations,$3, 4$ and $5$,were found to be incorrect. If the incorrect observations are omitted,then the variance of the remaining observations is

The coefficient of variation and standard deviation of an ungrouped data are $60$ and $21$ respectively. If $15$ is added to every observation of the data,then the coefficient of variation of the new data is

The $S.D.$ of $5$ scores $1, 2, 3, 4, 5$ is