A person standing on a railway platform noticed that a train took 21 seconds to completely pass through the platform which was 84 m long and it took 9 seconds in passing him. The speed of the train was Choose the correct option:
A) 25.2 km/hr B) 32.4 km/hr C) 50.4 km/hr D) 75.6 km/hr. E) None of these
Explanation:   Let the train’s length be L m.   L/9=(L+84)/21   21 L = 9L +756   12L= 756   L=63 m   Speed = 63 /9= 
<gadget id="calculator">63 /9</gadget>
<output>7</output>
7 m/s= 7 x 18/5 = 25.2 Km/hr.   25.2 km/hrnswer 25.2 km/hr
<result>A</result>
A person standing on a railway platform noticed that a train took 21 seconds to completely pass through the platform which was 84 m long and it took 9 seconds in passing him. The speed of the train was