This is one of my favorite math riddles. It requires no calculator, computer, or even pencil and paper. Just think about it!

A businessman commutes home from the office, and his train gets into the station in his home town exactly at the same time every day. Every day his chauffeur is there to pick him up and take him home, so that every day he arrives home at exactly the same time. Everything works like clockwork, so well in fact that the chauffeur is in the practice of timing his arrival at the station to exactly coincide with the arrival of the train.

One day, however, the businessman decides to leave work early, and he catches a train that gets to his station an hour early. He forgot to call ahead, so his chauffeur is not there to pick him up. The businessman decides that rather than wait for the chauffeur, he will start to walk home. Some time later the chauffeur comes driving along on his way to the station, sees his boss walking along the road, so he stops to pick him up, and they drive on home.

As the businessman walks in the front door of the house his wife exclaims, "Oh, honey, how nice -- you're home 20 minutes early!"

Question: how long was the man walking along the road before the chauffeur picked him up?

As usual with these types of problem, assume everything works nicely: constant velocity of the chauffeur's car, instant pick up and turn around, the train is always exactly on time, etc, etc.