A long train, half a kilometre long, is about to enter a long tunnel.
The tunnel is 10k long. If the speed of the train is 35kph, how long will it take for the entire train to pass through the tunnel - from the front of the train entering to the end of the train leaving the tunnel?
Answer: The train takes 18 minutes.
The front of the train has to initially travel 10k to leave the tunnel, and then a further 0.5k until the rear of the train has also left the tunnel - a total of 10.5k.
The train is travelling at 35kph and using Time = Distance ÷ Speed gives:
Time = 10.5 ÷ 35 = 0.3 hours.
Convert this to minutes:
0.3 x 60 = 18 minutes. QED.