How many 4 number combinations are there in the numbers 0 to 5?

Answer 1

The first digit can be one of five integers (1 to 5)

The second - fourth digits one of six integers (0 to 5).

So: number of (valid) combinations is 5*6*6*6=1080

* * * * *

This gives the number of permutations, not combinations. I am working on the latter.

Answer 2

If you are allowed to repeat letters (A-Z) then there are 17,576 different combinations. If you can not repeat letters then there are 15,600 combinations.

Answer 3

10