Two trains, each 100 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?

Let the speed of the slower train be x m/sec

So the speed of the faster train = 2x m/sec

So that the relative speed is = (x + 2x) m/sec

so ((100 + 100)/8) = 3x

200 = 24x

x= 25/3

so the speed of fast train 2x = 2*25/3

                                        = 50/3 m/sec = ((50/3)*(18/5))

                                        = 60 km/hr.