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 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 :

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

Which of the following show direct variation?

The standard deviation of the data 6, 5, 9, 13, 12, 8, 10 is