A bag contain `n` ball out of which some balls are white. If probability that a bag contains exactly `i` white ball is pro0portional to `i^3dot` A ball is drawn at random from the bag and found to be white, then find the probability that bag contains exactly 2 white balls.

Answer

`P (A_(2)//B) = (((6)/(n (n + 1))) ((2^(3))/(n)))/((2)/(3 (n + 1)))`