There are 9C3 = 84 combinations.
6 of them.
Only one.
How many four digit combinations can be made from the number nine? Example, 1+1+2+5=9.
120 combinations using each digit once per combination. There are 625 combinations if you can repeat the digits.
There are 15180 combinations.
10 Combinations (if order doesn't matter). 3,628,800 Possiblilities (if order matters).
It is: 9C7 = 36
10,000
15
6 ways: 931,913,139,193,391,319
Number of 7 digit combinations out of the 10 one-digit numbers = 120.