The Train Station
A man, John, always arrive to train station at 5pm everyday from work. John's driver always arrives to the train station at 5pm from John's house to pick him up. So, John & his driver always go back to John's house at the same time everyday.
One day, The train drove fast and John arrived at the train station at 4pm. Knowing that his driver wouldn't be at the train station until 5pm, he started to walk toward his house. At some point in time, John's driver saw John and picked him up. John & his driver got home 20 minutes earlier than usual time. How long has John been walking?
There isn't any trick or "I can't answer it because I need to know the arrival (to house) time". It is a straight and simple answer.