A train travelled a certain journey and is supposed to arrive at midday. When its average speed is 40km/h, it arrives at 1pm. When its average speed is 48km/h, it arrives at 11am. What is the length of the journey?
Let distance be d. d=vt where v is the speed and t the time. So d=40t=48(t-2), because 1pm-11am=2 hours. The reference time for t is 1pm, so t-2 is 11am. 40t=48t-96, 8t=96 so t=12 hours. And d=40×12=48×10=480 km. (To arrive at midday, the train’s speed would need to be 480/(t-1)=480/11 km/hr)
