How many different combinations can you make using 2 3 6 and 9?

Answer 1

If you use them only once each, you can make 15 combinations.

1 with all four digits,

4 with 3 digits,

6 with 2 digits, and

4 with 1 digit.

There is also a combination containing no digits making 16 = 24 combinations from 4 elements.