Two trains, each 50 m long, moving in opposite directions, cross each other in 4 seconds. If one is moving twice as fast the other, then the speed of the faster train is:

Question: Two trains, each 50 m long, moving in opposite directions, cross each other in 4 seconds. If one is moving twice as fast the other, then the speed of the faster train is:

Solution:
Let the speed of the slower train be x m/sec.
∴ speed of the faster train = 2x m/sec.

Relative speed = (x + 2x) m/sec = 3x m/sec.

Now,
(50 + 50)/4 = 3x
⇒ 12x = 100
⇒ x = 100/12
∴ x = 8.333

∴ speed of the faster train = 2 × 8.333 = 16.67 m/sec.