A farmer with a goat, cabbage and a wolf is standing on the side of a river. They need to cross it, but there is only a small row boat that only can fit two of them.
The goat is hungry, so if the farmer leaves the goat alone with the cabbage, the goat will eat the cabbage. The wolf is also hungry, and it will eat the goat if they are left alone.
How should the farmer proceed to get them all across the river?
Another answer to this puzzle: xkcd comic #1134.