A certаin pаsscоde is required tо be а sequence оf any 3 digits chosen from the ten digits followed by 1 letter chosen from the set {a, b, c, d, e}. (1) How many passcodes are possible if repetition of digits is allowed? [a1] (2) How many passcodes contain no repeated digits? [a2] (3) How many passcodes have at least one repeated digit? [a3] (4) What is the probability that a passcode chosen at random has at least one repeated digit, assuming that all passcodes are equally likely? (Please fill the blank with a numerical value in the form of m/n, where m and n are positive integers.) [a4] In (1), (2) and (3), please fill each blank with an integer and without comma or period.