3*3*3*3=81
24
500
There are 7,290 different 4-digit numbers that can be formed from the digits 1-9 without repetition.
There are 5*4*3 = 60 such numbers.
1 set
It is 120 if the digits cannot be repeated.
27 three digit numbers from the digits 3, 5, 7 including repetitions.
There are 5! = 120 such numbers.
27 if the digits can be repeated. 6 if not.
3x3x3=27
4*3*2*1 = 24
48 of them if digits may not be repeated. 100 if they can.