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).
10,000.
45
Assuming no duplication or repetition, 720
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.
You Can Create 999 Number combinations
10,000.
45
6
45 In combinations, the order of the digits does not matter so that 12 and 21 are considered the same.
Only one.
Assuming no duplication or repetition, 720
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
You Can Create 999 Number combinations
32C3 = 4960
Six combinations: 123, 132, 213, 231, 312, 321
100! / 97! = 100 * 99 * 98 = 970200