Using the digits 1, 3, 4, 5, 7, 8, 9. How many 4 digit numbers can be formed if 5, 7, and 9 must be included? Repetition of digits is not allowed.
How many 3 digit numbers can be formed using the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 if repetitions of digits are allowed?