$A$ multiple choice examination has $5$ questions. Each question has three alternative answers of which exactly one is correct. The probability that a student will get at least one correct answer is

The probability that a person who undergoes a bypass surgery will recover is $0.6$. The probability that of the $6$ patients who undergo similar operations,half of them will recover is:

$A$ fair coin is tossed $2n$ times. What is the probability that the number of heads and tails obtained in these $2n$ trials are not equal?

If the mean and variance of a binomial variate $X$ are $2$ and $1$ respectively,then the probability that $X$ takes a value greater than $1$ is

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 $90 \%$?

Numbers are selected at random,one at a time from two-digit numbers $10, 11, 12, \ldots, 99$ with replacement. An event $E$ occurs if and only if the product of the two digits of a selected number is $18$. If four numbers are selected,then the probability that the event $E$ occurs at least $3$ times is