500
It is 120 if the digits cannot be repeated.
4*3*2*1 = 24
6*5*4*3*2*1=720
That would be 4! = 4 * 3 * 2 * 1 = 24
24
500
There are 5*4*3 = 60 such numbers.
1 set
It is 120 if the digits cannot be repeated.
There are 7,290 different 4-digit numbers that can be formed from the digits 1-9 without repetition.
This permutation problem depends on whether the numbers are allowed to be repeated. If they are, there are a possible 9999 numbers, starting with 0001 and running sequentially to 9999. If they are not allowed to be repeated, there are a possible 5040 combinations.
3x3x3=27
36
6*6*3 = 108 numbers.
4*3*2*1 = 24
6*5*4*3*2*1=720 possible numbers