(a) How many 4-digit numbers are there without repetition of digits?

(b) How many 4-digits are there, if there is no restriction on repetition of digits?

(c) How many 4-digit numbers are there with at least one number repeated?

How many 3-digit even numbers can be made using the digits 1, 2, 3, 4, 6, 7, if no digit is repeated?

(a) no student gets more than one prize?

(b) any student may get any number of prize (s)?

(c) no student may get all prizes?