Let $X \sim B(n, p)$. If $E(X) = 2$ and $Var(X) = 1$, then the probability of getting at most one success is .....

$7$ coins are tossed simultaneously and the number of heads turned up is denoted by the random variable $X$. If $\mu$ is the mean and $\sigma^2$ is the variance of $X$,then $\frac{\mu \sigma^2}{P(X=3)}=$

$A$ pair of fair dice is thrown $4$ times. If getting the same number on both dice is considered as a success,then the probability of exactly two successes is:

The probability of a bomb hitting a bridge is $1/2$ and two direct hits are needed to destroy it. Find the least number of bombs required so that the probability of the bridge being destroyed is greater than $0.9$.

For a binomial variate $X$ with $n=6$,if $P(X=2)=9 P(X=4)$,then its variance is

Let $X \sim B(n, p)$ with mean $\mu$ and variance $\sigma^2$. If $\mu=2 \sigma^2$ and $\mu+\sigma^2=3$,then $P(X \leq 3)=$