14. (a) An urn contains $m$ white and $n$ black balls. A ball is drawn at random and is put back into the urn along with k additional balls of the same colour as that of the ball drawn. A ball is again drawn at random. What is the probability that the ball drawn now is white? (b) An unbiased die, with faces numbered $1,2,3,4,5,6$ is thrown n times and the list of n numbers showing up is noted. What is the probability that, among the numbers $1,2,3,4,5,6$ only three numbers appear in this list?
14. (a) An urn contains $m$ white and $n$ black balls. A ball is drawn at random and is put back into the urn along with k additional balls of the same colour as that of the ball drawn. A ball is again drawn at random. What is the probability that the ball drawn now is white?\\
(b) An unbiased die, with faces numbered $1,2,3,4,5,6$ is thrown n times and the list of n numbers showing up is noted. What is the probability that, among the numbers $1,2,3,4,5,6$ only three numbers appear in this list?\\