hr. 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?

A. 66 km/hr

B. 72 km/hr

C. 78 km/hr

D. 81 km/hr

View Answer

Correct Answer :
81 km/hr

Explanation :

Converting km/hr into m/sec

4.5 km/hr = (4.5 x 5/18) m/sec = (5/4) m/sec = 1.25 m/sec

5.4 km/hr = (5.4 x 5/18) m/sec = (3/2) m/sec = 1.5 m/sec

Let the speed of the train be x m/sec

Then, (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

=> Speed of the train = 22.5 x (18/5) km/hr = 81 km/hr

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