POW #4: Mr. Smith's Journey Home

Mr. Smith, a commuter, is picked up each day at the train station at exactly 5 o'clock. One day he arrived unannounced on the 4 o'clock train and began to walk home. Eventually he met the chauffeur driving to the station to get him. The chauffeur drove him the rest of the way home, getting him there 20 minutes earlier than usual.

On another day, Mr. Smith arrived unexpectedly on the 4:30 train, and again began walking home. Again he met the chauffeur and rode the rest of the way with him. How much ahead of usual were they this time? (Assume constant speeds, and that no time is lost turning the car around and picking up Mr. Smith.)

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