If the mean and standard deviation of a binomial distribution are $20$ and $4$,respectively,then the number of trials is $.......$

If $20 \%$ of the bolts produced by a machine are defective, then the probability that out of $4$ bolts chosen at random, less than $2$ bolts will be defective, is

$A$ rifleman is firing at a distant target and has only $10 \%$ chance of hitting it. The least number of rounds he must fire to have more than $50 \%$ chance of hitting it at least once, is

The probability mass function of a random variable $X$ is given by $P(X = x) = \frac{^5C_x}{2^5}$, for $x = 0, 1, 2, 3, 4, 5$ and $0$ otherwise. Which of the following is correct?

$A$ fair coin is tossed a fixed number of times. If the probability of getting $7$ heads is equal to the probability of getting $9$ heads,then the probability of getting $2$ heads is:

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