1) A password for computer includes four characters. Each character might be a digit, an uppercase (or capital) letter or a lowercase (small) letter, and characters may be repeated.
a) Determine the number of possible passwords.
b) If you forget the password and make random guess, determine the probability that you guess the correct password.
c) If you forget the last character of the password, but remember the first three, determine the probability that you guess the correct password.