2.4.6 Let X0;X1;X2; : : : be independent identically distributed nonnegative random variables having a continuous distribution. Let N be the first index k for which Xk > X0. That is, N D 1 if X1 > X0;N D 2 if X1  X0 and X2 > X0, etc. Determine the probability mass function for N and the mean E[N]. (Interpretation:

X0;X1; : : : are successive offers or bids on a car that you are trying to sell. Then, N is the index of the first bid that is better than the initial bid.)