The probability that an event does not happen in one trial is $0.8$. The probability that the event happens at most once in three trials is:

In a binomial distribution,the probability of success is $\frac{1}{4}$ and the standard deviation is $3$. Then,its mean is

$A$ box has $100$ pens of which $10$ are defective. The probability that out of a sample of $5$ pens drawn one by one with replacement,at most one is defective is:

$A$ 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:

$A$ bag contains $30$ white balls and $10$ red balls. $16$ balls are drawn one by one randomly from the bag with replacement. If $X$ is the number of white balls drawn,then $\left( \frac{\text{mean of } X}{\text{standard deviation of } X} \right)$ is equal to

$A$ die is thrown $6$ times. If 'getting an odd number' is a success,what is the probability of $5$ successes?