A Nobel Prize winning mathematician is traveling from university to university on a speaking tour by limousine. After several engagements the mathematician and his driver are having dinner and the driver says "I've heard your speech so many times I think I could give it word-for-word." The mathematician accepts the challenge and they switch places for the next speech; the driver dresses like the professor and the professor dresses as the driver and sits in the back of the auditorium.
The driver gives the speech flawlessly and opens up the floor for questions, usually there are none. But one of the students at the university has a very large ego and decides to attempt to stump the Nobel Prize winner. After the student asks his question for ten straight minutes the driver laughs and says "That question is so simple I'll let my driver in the back answer it."