$A$ coin is tossed $4$ times. The probability that at least one head turns up is

$A$ fair coin is tossed $n$ times. Let $X$ be the number of times head is observed. If $P(X = 4), P(X = 5)$ and $P(X = 6)$ are in $H.P.$,then $n$ is equal to

$8$ coins are tossed simultaneously. The probability of getting at least $6$ heads is

Two cards are drawn successively with replacement from a well-shuffled pack of $52$ cards. The mean of the number of kings is:

If the half-life period of a substance is $5 \text{ years}$, then the total amount of the substance left after $15 \text{ years}$, when the initial amount is $64 \text{ g}$, is: (in $\text{g}$)

If the mean and variance of a binomial variate $X$ are $2$ and $1$ respectively,then the probability that $X$ takes a value greater than $1$ is