-59
6
10
Six combinations: 123, 132, 213, 231, 312, 321
120 combinations using each digit once per combination. There are 625 combinations if you can repeat the digits.
Only one.
45
6
10
32C3 = 4960
Six combinations: 123, 132, 213, 231, 312, 321
Assuming you are treating each number as a number and not as an individual unit, the numbers you can make from these digits are 899, 989 and 998.
There are 167960 9 digits combinations between numbers 1 and 20.
Assuming the digits cannot be repeated, there are 7 combinations with 1 digit, 21 combinations with 2 digits, 35 combinations with 3 digits, 35 combinations with 4 digits, 21 combinations with 5 digits, 7 combinations with 6 digits and 1 combinations with 7 digits. That makes a total of 2^7 - 1 = 127: too many for me to list. If digits can be repeated, there are infinitely many combinations.
10,000.
∞ \ Infinite
120 combinations using each digit once per combination. There are 625 combinations if you can repeat the digits.
5040, assuming none of the digits are the same. (Assuming they're not, there's 5040 unique combinations you can make out of 7 digits).