A credit card contains 16 digits. It also contains a month and year of expiration. Suppose there are one million users of a credit card with unique card numbers. A hacker randomly selects a 16 digit credit card number.
(a) What is the probability that it belongs to a user?
(b) Suppose a hacker has a 25% chance of correctly guessing the year your card expires and randomly selects one of the 12months. What is the probability that the hacker correctly selects the month and year of expiration?