Monday, February 11th, 2013
Question : Without stoppage, a train travels at an average speed of 75km/h. With stoppages it covers the same distance at an average speed of 60 km/h. How many minutes per hour does the train stop?
This seems like a pretty straightforward question but can confuse because of the way it is asked. The best way to understand it, in my opinion, is to assume a distance.
Let us say that the distance that the train covers is 300 km. (I am taking 300 km because it is divisible by both 75 & 60)
Case 1: Time taken without stoppages = 300 / 75 = 4 hours.
Case 2: Time taken with stoppages = 300 / 60 = 5 hours.
In the second case, the train was moving for 240 minutes and static for 60 minutes. So, the ratio of stopped time to motion time is 60:240 or 1:4.
=> The train stops for 1/5th of the time traveled. Thus the train stops for 12 minutes per hour.