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 $0.9$.

Two dice are thrown $5$ times,and each time the sum of the numbers obtained being $5$ is considered a success. If the probability of having at least $4$ successes is $\frac{k}{3^{11}}$,then $k$ is equal to

The probability of a man hitting a target is $\frac{2}{5}$. He fires at the target $k$ times ($k$ is a given number). The minimum value of $k$ such that the probability of hitting the target at least once is more than $\frac{7}{10}$ is:

$A$ die is thrown $100$ times. If the success is defined as getting an even number,then the variance of the number of successes is:

Let in a Binomial distribution,consisting of $5$ independent trials,probabilities of exactly $1$ and $2$ successes be $0.4096$ and $0.2048$ respectively. Then the probability of getting exactly $3$ successes is equal to

$A$ person buys a lottery ticket in $50$ lotteries,in each of which his chance of winning a prize is $\frac{1}{100}$. What is the probability that he will win a prize exactly once?