A COMMUTER IS in the habit of arriving at his suburban station each evening
exactly at five o’clock. His wife always meets the train and drives him home.
One day he takes an earlier train, arriving at the station at four. The weather is
pleasant, so instead of telephoning home he starts walking along the route
always taken by his wife. They meet somewhere on the way. He gets into the car
and they drive home, arriving at their house ten minutes earlier than usual.
Assuming that the wife always drives at a constant speed, and that on this
occasion she left just in time to meet the five o’clock train, can you determine
how long the husband walked before he was picked up?