Federal Express is a company that ships packages from one city to another by airplane. In the United States it uses a system that might at first glance seem very odd and inefficient. The challenge of this puzzle is to understand why the company uses these routes.

If you are sending a package from New York City, the blue dot, to Boston, the green dot, it first goes by plane to Memphis, the red dot, and then on to Boston. Similarly, a package going from Los Angeles, yellow dot, to San Francisco, light blue dot, also goes through Memphis. Packages from cities all over the USA are brought to Memphis, where they are sorted according to their destinations. Then each plane returns to the city it came from loaded with packages for delivery there.

But it’s shorter to go directly from New York to Boston and from Los Angeles to San Francisco than going through Memphis. How can all this extra air travel make sense?