College Professor

The Old Professor asked his college class a question.

"If Philadelphia is 100 miles from New York and Chicago is 1000 miles from Philadelphia and Los Angeles is 2000 miles from Chicago and the Moon is 239,000 miles from Earth, how old am I?"

Pauly in the back of the class raised his hand and when called upon said, "Professor you're 60."

The Professor said, "You're absolutely correct, but tell me, how did you arrive at the answer so quickly?"

Pauly replied, "You see, I have a brother; he's 30, and he's half nuts."