If three letters can be posted to any one of the $5$ different addresses, then the probability that the three letters are posted to exactly two addresses is:

Three numbers are chosen at random from $1$ to $15$ . The probability that no two numbers are consecutive, is

Three squares of a chess board are chosen at random, the probability that two are of one colour and one of another is

A bag contains $4$ white, $5$ red and $6$ green balls. Three balls are picked up randomly. The probability that a white, a red and a green ball is drawn is

Let $S$ be the sample space of all five digit numbers.If $p$ is the probability that a randomly selected number from $S$, is a multiple of $7$ but not divisible by $5$ , then $9\,p$ is equal to.

Four persons independently solve a certain problem correctly with probabilities $\frac{1}{2}, \frac{3}{4}, \frac{1}{4}, \frac{1}{8}$. Then the probability that the problem is solved correctly by at least one of them is