An ordinary 6-sided die has a number on each face from 1 to 6 (each number appears on one face). How many ways can I paint two faces of a die red, so that the numbers on the red faces don't add up to 7?
We have C(6,2) = 15 possibilites
They are
1,2 2,3 3,4 4,5 5,6
1,3 2,4 3,5 4,6
1,4 2,5 3,6
1,5 2,6
1,6
Only 1,6 2,5 and 3,4 add to 7
So....there are 12 ways to paint the faces so that the numbers do not add to 7
I see. Thanks!
