You have two empty bags and 100 bread rings. The goal is to put all your rings into the bags in such a way that one of the bags will contain exactly twice as many rings then the other.
You can't eat, break and lose the rings. All of them should go into the bags.
Let me know if my explanation is not clear.
Actually, I know the answer but I'd like to share it with you. IMHO, it is pretty nice.