The last will of a horse breeder is that all his horses are to be given to his three children in the following ratio: 1/2:1/3:1/9. At the moment the horse breeder passed away he owned 17 horses. How could his last will be followed?

Mom, Dad, and two kids have come to a river, and they find a boat. It is small and can only carry one adult or two kids at a time. Both kids are good rowers, but how can the whole family reach the other side of the river?

A jeweller has three boxes: A, B and C. Each box contains three rings, which are either all made of pure gold, or all fake. The fake rings weight 1 gram less then the real ones. It is known that a least one of the boxes contains fake rings. The jeweller has a balance with three weights of exactly 1 gram. Is it possible that the jeweller finds out which box(es) contain the fake rings with weighing only once? And if so, how does she do it? (We define weighing only once that only once a situation is reached in which the balance is in equilibrium.)