A mischievous student wants to break into a computer file, which is password-protected. Assume that there are n passwords only one of which is correct, and that the student tries possible passwords in a random order. Let N be the number of trials required to break into the file. Determine the pmf of a) if unsuccessful passwords are not eliminated from further selections, and b) if they are eliminated. c) If n = 10, what is the expected number of trials in each case (a) and (b)