arithmetic - two trains each 140 m long moving in opposite directions cross each other in 7 seconds if one is moving thrice as fast the other then the speed of the faster train is - skillgun

let the speed of the slower train be x m/sec.
then, speed of the faster train be 3x m/sec.
relative speed = (x +3x) m/sec = 4x m/sec.
.'. (140 +140)/7 = 4x <=> 280 = 28x => x = 10 m/sec.
so, speed of the faster train = ((3*10) * 18/5) km/hr = 108 km/hr.