My son's homework said, 'If a train leaves Station A at 60 miles per hour and another train leaves Station B at 40 miles per hour, heading toward each other, when do they meet?' I did the math. He looked at me and said, 'Dad, trains do not leave stations at 60 miles per hour.' I said, 'This is a thought experiment.' He said, 'The train is in the picture. It has a cab. It has wheels. It is not a thought. I saw a train last week. It left the station at the speed of a man walking to the mailbox. The answer is not two hours. The answer is eventually, and probably not today.'