A man in a train notices that he can count 21 telephone posts in one minute.If they are known to be 50 meters apart , then at what speed is the train travelling ?  Pick:
A) 55 km/hr
B) 57 km/hr
C) 60 km/hr
D) 63 km/hr
E) None of these
Solution   Number of gaps between 21 telephone posts = 20.   Distance travelled in 1 minute =(50x20)m = 1000 m = 1 km.   ∴ Speed = 60 km/hr.   Answer 60 km/hr
<result>C</result>
A man in a train notices that he can count 21 telephone posts in one minute.If they are known to be 50 meters apart , then at what speed is the train travelling ?