Two trains, each 150 m long, moving in opposite directions, cross each other in 8 seconds. If one is moving twice as fast the other, then the speed of the faster train is:

Question: Two trains, each 150 m long, moving in opposite directions, cross each other in 8 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
(150 + 150​)/8 = 3x
300/8 = 3x
100/8 = x
x = 25/2

Speed of the faster train =(25​/2) × 2 m/sec
= 25​ × (18​/5)km/hr
= 90 km/hr.