The standard deviation of the numbers $22, 26, 28, 20, 24, 30$ is

For any integer $n \geq 1$,the sum $\sum_{k=1}^n k(k+2)$ is equal to

When a $p-n$ diode is reverse biased,then

The median of a set of $9$ distinct observations is $20.5$. If each of the largest $4$ observations of the set is increased by $2$,then the median of the new set

Which of the following is arranged in decreasing order of size?

Let $\alpha \neq 1$ be a real root of the equation $x^3-ax^2+ax-1=0$,where $a \neq -1$ is a real number. Then,a root of this equation,among the following,is