We are making passwords in such a way that each character in the password is a digit or an uppercase letter. (a)
(4 points) How many such passwords of length n are there?
(b) (4 points) How many passwords of length 10 start with a digit?
(c) (5 points) What is the probability that a random password of length 20 contains at least one digit?
(d) (5 points) What is the probability that a random password of length 20 contains exactly three digits?