Talking of time I just recalled another puzzling question about time. Consider this:
Mohan lives 24 km from the railway station. He has one hour to catch the train. He leaves home at the speed of 18 km/hr. Travels half the distance and then increases his speed to 30km/hr. He with this speed for the next quarter of the distance and then plans to speed up again. Now what should be his speed in order to catch the train.