Railway Announcement
In an announcement on a railway station, a passenger hears that the last train has passed the station 30 minutes earlier than his train. On the next station that is 20 km away from the previous station, in the other announcement he hears that the first train arrives 20mins earlier than his train. Reading from his watch, he calculates average speed of the train viz. 60 km/hr. Determine the average speed of the first train.
The answer is 40.
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1 solution
From the announcements, the passenger gathers that the previous train left 30 minutes and arrived 20 minutes earlier than those of his own train. Thus, that train took 10 minutes more for the distance of the 2 stations (20 km) than it would the train he was on. His own journey took 20(60/60) = 20 minutes, so that other train moves 20 km in 20+10=30 minutes, a speed of 20/(30/60) = 40 kmph.