$A$ die is thrown four times. The probability of getting a perfect square in at least one throw is

The probability that a marksman will hit a target is given as $1/5$. Then his probability of at least one hit in $10$ shots is:

Mean and variance of a binomial probability distribution are $4$ and $\frac{4}{3}$ respectively. Then the probability of at least two successes is equal to:

An urn contains $25$ balls of which $10$ balls bear a mark $'X'$ and the remaining $15$ bear a mark $'Y'$. $A$ ball is drawn at random from the urn,its mark is noted down and it is replaced. If $6$ balls are drawn in this way,find the probability that not more than $2$ will bear $'Y'$ mark.

The minimum number of times a fair coin must be tossed so that the probability of getting at least one head is more than $99\%$ 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: