A peasant has to cross a river with а wolf, a goat, and a cabbage. The boat can carry the peasant with only one more item in a trip.
The goat if left with the grass will eat it. If the wolf and the goat are left behind, the wolf will eat the goat.
How does peasant get them all across the river safely?
After that, he goes with wolf, leaves it, comes with goat.
Then he goes with cabbage, leaves it with wolf, comes back.
Finally he goes with goat.