If $X \sim B(4, p)$ and $P(X=0)=\frac{16}{81}$,then $P(X=4)=$

The probability that a person will develop immunity after vaccination is $0.8$. If $8$ people are given the vaccine,then the probability that all develop immunity is equal to:

In an examination,there are $10$ true-false type questions. Out of $10$,a student can guess the answer of $4$ questions correctly with probability $\frac{3}{4}$ and the remaining $6$ questions correctly with probability $\frac{1}{4}$. If the probability that the student guesses the answers of exactly $8$ questions correctly out of $10$ is $\frac{27 k}{4^{10}}$,then $k$ is equal to

The probability of a man hitting a target is $3/4$. He tries $5$ times. What is the probability that he hits the target at least $3$ times?

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

If the mean and variance of a binomial variate $X$ are $8$ and $4$ respectively,then $P(X < 3)$ equals to