A river, a small boat and three passengers who cannot stay with just any company. The farmer will have to come and go more times than seems necessary.
The wolf, the goat and the cabbage
Riddle statement
A farmer must cross a river with a wolf, a goat and a cabbage. The boat can only carry the farmer and one of the other three.
If you leave the wolf alone with the goat, the wolf eats it. If you leave the goat alone with the cabbage, the goat will eat it.
How can everyone cross without either of those things happening?