A successful businessman visted his old economics professor. While chatting, the former student noticed an exam on the professor's desk and began reading. Shocked, he announced, "This is the same exam you gave me fifteen years ago! Aren't you afraid the students are just going to track down old tests?" The professor laughed. "No, that's okay. I do keep the same questions. It's the answers I change every year."

--- Todd Bucholtz in "New ideas from dead economists", 1989, p 236