If the probabilities of a boy and a girl being born are the same,then in a $4$-children family,the probability of having at least one girl is:

When six coins are tossed simultaneously,the probability of getting at least $4$ heads is

For Binomial distribution $B \left(10, \frac{1}{2} \right)$,if $P(X \leq 2) = m \left( \frac{1}{2} \right)^{10}$,then $m =$ . . . . . . .

$A$ man makes attempts to hit the target. The probability of hitting the target is $\frac{3}{5}$. Then the probability that he hits the target exactly $2$ times in $5$ attempts is:

The probability that a bulb produced by a factory will fuse after $150$ days of use is $0.05$. What is the probability that out of $5$ such bulbs,none will fuse after $150$ days of use?

The discrete random variables $X$ and $Y$ are independent from one another and are defined as $X \sim B(n_1, 0.5)$ and $Y \sim B(n_2, 0.4)$. If the variance of both $X$ and $Y$ is $6$,then $\sqrt{n_1+n_2}=$