Two trains of equal length, running in opposite directions, pass a pole in 18 and 12 seconds. The trains will cross each other in ?



Two trains of equal length, running in opposite directions, pass a pole in 18 and 12 seconds. The trains will cross each other in ?

A. 14.4 sec

B. 15.5 sec

C. 18.8 sec

D. 20.2 sec

Answer : A. 14.4 sec


Explanation :

    Let length of each train be x meter.
    Then, speed of 1st train = x/18 m/sec
    Speed of 2nd train = x/12 m/sec

    Now, When both trains cross each other, time taken
    = [ 2x/((x / 18 ) + (x / 12)) ]
    = 2x / [(2x + 3x) / 36] = 2x * 36 / 5x
    = 72 / 5
    = 14.4 seconds.


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