一道英语数学题

题目

一道英语数学题
A woman arrives at the station at the same time every day.Her husband drives from home to the station to pick her up.They always arrive back at their house at the same time every day,driving at the same speed.One day she arrives at the station one hour early and starts to walk home.Her husband meets her along the road and they arrive home together.They arrived home ten minutes earlier than usual.Assuming all speeds of walking and driving are constant and all transfers are immediate,how long had the woman been walking when her husband meet her?（ ）
（answer in minutes）
（A）10 （B）50 （C）55 （D）70 （E）90

答案

c
60-10/2=55