>>Ok, need to think more...
>
>You're thinking too much.
>You've got balls in group A, B and C.
>Two of those groups will weigh the same. The third group will weigh different. Stick to weighing more in that group.

If A=B, then the solution is trivial. If A<>B, the solution is more complicated. Dan gave it in another thread, but I didn't think it through...

Anyway, here is a simple problem for you.

Two players play the game: who first says 100 will win. They can say any number between 1 and 10. Who and how will win?

Example:
A - 3
B - 7
A - 9
B - 10
etc.