A good express train and a overtaking express train are travelling on parallel tracks in the same direction. The driver of the goods express train observes that the overtaking express train coming from behind overtakes and passes his express train completely in 60 sec. Whereas a overtaking on the overtaking express train marks that he passes the goods express train in 40 sec. If the speeds of the express trains be in the ratio 1:2. Find the ratio of their lengths.