Mean and standard deviation of a data are $48$ and $12$ respectively. The coefficient of variation is.

If the probability of X to fail in the examination is 0.3 and that for Y is 0.2, then the probability that either X or Y fails in the examination is :

If $A$ and $B$ are two independent events such that $P(A)=\dfrac{1}{3}$ and $P(B)=\dfrac{3}{4}$, then $p\left\{\dfrac{B}{(A\cup B)}\right\}$

If $\mathrm{A}$ and $\mathrm{B}$ are two events such that $P(\displaystyle \mathrm{A}\cup B)\geq\frac{3}{4}$ and $\displaystyle \frac{1}{8}\leq P(\mathrm{A}\cap B)\leq\frac{3}{8}$ then

Two sets each of $20$ observations, have the same standard deviation $'5'$. The first set has a mean $'17'$ and the second set mean $'22'$ then standard deviation of the combining the given two sets is