The probability of a man hitting a target is $\frac{1}{10}$. The least number of shots required,so that the probability of his hitting the target at least once is greater than $\frac{1}{4}$,is

There are $800$ families with four children in each family. Assuming an equal chance for every child to be a boy or a girl,the number of families expected to have children of both sexes is:

The binomial distribution whose mean is $9$ and whose standard deviation is $\frac{3}{2}$ is equal to

If the probability of hitting a target by a shooter,in any shot,is $\frac{1}{3}$,then the minimum number of independent shots at the target required by him so that the probability of hitting the target at least once is greater than $\frac{5}{6}$,is

$A$ fair coin is tossed $99$ times. If $X$ is the number of times head occurs,then $P[X=r]$ is maximum when $r=$

The probability of a man hitting a target is $\frac{2}{3}$. What is the minimum number of times he must fire so that the probability of hitting the target at least once is more than $90 \%$?