Have you heard the one about an itinerant entertainer traveling with a wolf, a goat, and a basket of cabbages?
The showman comes to a river and finds a small boat that holds only himself and one passenger. For obvious reasons, he can't leave the wolf alone with the goat, or the goat with the cabbages. How does he get his cargo safely to the other side?
The showman would need seven trips to ferry the cabbages, goat, and wolf across the river. The showman crosses the river with the goat and leaves the goat on the far shore, then returns alone to the near shore. He brings the wolf to the far shore and brings the goat back to the near shore. He then brings the cabbages to the far shore and returns alone to the near shore. Finally, the showman brings the goat to the far shore.
Another solution interchanges the wolf and the cabbages.