Riddle: A Fox, A Sheep, and A Sack of Hay
A farmer is travelling with a fox, a sheep and a small sack of hay. He comes to a river with a small boat in it. The boat can only support the farmer and one other animal/item. If the farmer leaves the fox alone with the sheep, the fox will eat the sheep. And if the farmer leaves the sheep alone with the hay, the sheep will eat the hay.
How can the farmer get all three as well as himself safely across the river?
Given that the fox would eat the sheep, and the sheep would eat the hay (if given the chance), there is only one possible first move for the farmer.