Two trains each 180meter long moving in opposite directions cross each other in 12 seconds If one is...........

Quantitative Aptitude (CDS) Problems on trains

Two trains, each 180meter long, moving in opposite directions, cross each other in 12 seconds. If one is moving twice as fast as the other, then the speed of the faster train is?

72kmph

68kmph

50kmph

55kmph

Explanation:

Let the speed of the slower train be x m/sec
Then, speed of the faster train = 2x m/sec
Relative speed = (x+2x)m/sec = 3xm/sec
(18+180)/12= 3x
36x = 360
x = 360/36 = 10
So, speed of the faster train = 2×10 m/sec = 20m/sec
= 20×18/5 kmph
= 72kmph