Two trains of lengths 150 m and 250 m run on parallel lines. When they run in the same direction, they take 20 seconds to cross each other and, when they run in the opposite direction, they take 5 seconds to cross each other. What is the speed of the two trains?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 180 km/h and 108 km/h.
Let the speed of the faster train = x m/sec and the speed of the slower train = y m/sec
Total distance to be covered = 150 + 250 = 400 m
So, 20(x - y) = 400
⇒ x - y = 20 .....(1)
Also, 5(x + y) = 400
⇒ x + y = 80 .....(2)
Adding equations (1) and (2),
2x = 100
⇒ x = 100/2 = 50
Putting the value of x in equation (1),
50 - y = 20
⇒ y = 50 - 20 = 30
The speed of the faster train = 50 m/sec = 50 × (18/5) km/h = 180 km/h
The speed of the slower train = 30 m/sec = 30 × (18/5) km/h = 108 km/h
Therefore, the speeds of the two trains are 180 km/h and 108 km/h.