An old chestnut
goes like this:
A farmer as transporting a wolf, a goat, and a basket of cabbages. (Don't ask why he has a wolf with him.) He comes to a great river. He has only a small boat available, which can only hold him and one other item (wolf, goat, or cabbages) at a time. However, he knows that the wolf will eat the goat if they are left alone together, and likewise the goat will eat the cabbages. (The wolf is carnivorous and will not touch the cabbages.) How can he get the wolf, goat, and cabbages across the river without anything being eaten?