Each day a man meets his wife at the train station after work, and then she drives him home. She always arrives exactly on time to pick him up. One day he catches an earlier train and arrives at the station an hour early. He immediately begins walking home along the same route the wife drives. Eventually his wife sees him on her way to the station and drives him the rest of the way home. When they arrive home the man notices that they arrived 20 minutes earlier than usual. How much time did the man spend walking?
A) 45 minutes
B) 50 minutes
C) 40 minutes
D) 55 minutes
E) 35 minutes
This isn't so hard if you look at it from another perspective.
We know that the wife left at the time that she normally leaves, because she had no idea that the husband had arrived early. We know that the wife and husband arrived home 20 minutes earlier than usual, even though the wife left home at the regular time. For them to arrive home 20 minutes early, the wife would have had to have encountered the husband after he had walked the distance covered by 10 minutes of travel in a car. 20 minutes would be saved because the wife would save the 10 minutes that would have been required to drive from the point she saw her husband to the station, as well as the ten minutes back from the station to the point she saw her husband.
So, let's say the husband usually arrives at 3pm. Today he arrives at 2pm. The wife leaves 2:30pm to pick him up. She will meet up with the husband at 2::50 pm, because of the above analysis (by meeting up with him at 2:50, rather than her normal 3 o'clock meeting, she saves 10 minutes from husband to station, and back from station to husband, and they arrive home 20 minutes early, as stated in the facts.
So, husband begins walking at 2pm, and wife meets up with him at 2:50=50 minutes. It does not matter which numbers you plug in for the time, the result is always the same. If husband arrives usually at 4:30pm, then that means today he arrived at 3:30 pm. Wife needs to meet up with him at 4:20 pm to save the 20 minutes back and forth. 3:30-4:20=50 minutes.