Two people strolling along a railway track are overtaken by a train. The first one walks at a speed of 4.5 kilometres per hour. The other walks at a speed of 5.4 km/hr. The train takes 8.4 and 8.5 seconds to pass them, respectively. If both people are walking in the same direction as the train, what is the train's speed?
A. 66 km/hr
B. 72 km/hr
C. 78 km/hr
D. 81 km/hr
Answer:D
Two people strolling along a railway track are overtaken by a train. The first one walks at a speed of 4.5 kilometres per hour. The other walks at a speed of 5.4 km/hr. The train takes 8.4 and 8.5 seconds to pass them, respectively. If both people are walking in the same direction as the train, what is the train's speed?
A. 66 km/hr B. 72 km/hr C. 78 km/hr D. 81 km/hr
Explanation: 4.5 km/hr equals (4.5 x 5/18 ) m/sec = 5/4 m/sec = 1.25 m/sec, while 5.4 km/hr equals (5.4 x 5/18 ) m/sec = 3/2 m/sec = 1.5 m/sec.Let's say the train's speed is x m/sec.Consequently, (x - 1.25) x 8.4 = (x - 1.5) x 8.5 => 8.4x - 10.5 = 8.5x - 12.75 => 0.1x = 2.25 => x = 22.5.As a result, the train's speed is ( 22.5 x 18/5 ) km/hr = 81 km/hr.