A guy has two girlfriends: en the East and the West. He works near 5 Points Marta station and finishes his job at a random time of the day. Rather than deciding to which of two girls take the train - he leaves the choice to a chance: he takes the train (East or West) whichever comes first. The west train comes every 10 min and the East train comes every 10 min throughout the day. Nevertheless, after half a year he finds out that he is coming to east girl several time more frequently than to the West girl. Why???

Please give me an algorithm