Question

Tre rolls two standard six-sided number cubes. How many ways can he roll a sum of 7?

Answer 1

\[nCr = \frac{n!}{r! (n - r)!}\]

This is a combination, but in this case it's simpler just to think about it, as there's not many:
1+6=7
6+1=7
2+5=7
5+2=7
3+4=7
4+3=7

Answer 2

Make sense?