Two university students had an exam coming up but they opted to party instead, and missed the test. “Our car broke down due to a flat tyre,” they told the professor earnestly. “Can we write the exam tomorrow?” The professor agreed to give them a makeup test the next day.

Both boys crammed all night until they were sure they knew just about everything. Arriving the next morning, each was told to go to a separate classroom to take the exam. They shrugged and complied. As they sat down, they read the first question: “For 5 points, explain the contents of an atom.” This is going to be a piece of cake! thought each boy, answering the question with ease.

Then, the test continued. “For 95 points, tell me which tyre it was.”