In Letters to a Young Mathematician, Ian Stewart wrote:
I am reminded of one of the many stories mathematicians tell each other after all the nonmathematicians leave the room. A mathematician at a famous university went to look around the auditorium, and when she got there, she found the dean of the faculty staring at the ceiling and muttering to himself, "... forty-five, forty-six, forty-seven..." Naturally she interrupted the count to find out what it was for. "I'm counting the lights," said the dean. The mathematician looked up at the perfect rectangular array of lights and said, "That's easy, there are twelve that way, and... eight that way. Twelve eights are ninety-six." "No, no," said the dean impatiently. "I want the exact number."