… and my brother drives a Cadillac, how old am I?”
“You are eighty-four,” replied Mulla Nasruddin promptly.
“Right,” said the professor. “Now tell the rest of the fellows here how you arrived at the correct answer.”
“It is easy,” said Nasruddin. “I have got an uncle who is forty-two, and he is only half nuts. You must be eighty-four.”