A train overtakes two persons walking along a railway track. The first one walks at 4.5 km/h. The other one walks at 5.4 km/h. The train needs 8.4 and 8.5 seconds respectively to overtake them. What is the speed of the train if both the persons are walking in the same direction as the train?  Choose the most appropriate option:  A) 66 km/h  B) 72 km/h  C) 78 km/h  D) 81 km/h  E) None of these
4.5 km/h = (4.5 × 5⁄18) m/sec = 1.25 m/sec.   &amp; 5.4 km/h = (5.4 × 5⁄18) m/sec = 1.5 m/sec.   Let the speed of the train be S m/sec.   Then, (S – 1.25) × 8.4 = (S – 1.5) × 8.5   ⇒ 8.4S – 10.5 = 8.5S – 12.75 ⇒ 0.1S = 2.25 ⇒ S = 22.5.   ∴ Speed of the train = (22.5 × 18⁄5) km/h = 81 km/h   Answer 81 km/h
<result>D</result>
A train overtakes two persons walking along a railway track. The first one walks at 4.5 km/h. The other one walks at 5.4 km/h. The train needs 8.4 and 8.5 seconds respectively to overtake them. What is the speed of the train if both the persons are walking in the same direction as the train?