A college professor asked his class a question. If Philadelphia is 100 miles from New York and Chicago is 1000 miles from Philadelphia and Los Angles is 2000 miles from Chicago, how old am I.

One student in the back of the class raised his hand and when called upon said 'Professor your 44..'

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

The student said. 'You see professor I have a brother, he's 22 and he's half mad.'