Question

Standing on the side of a railway track a man found that two trains of same length crossed him in opposite directions in 18sec and 12 sec respectively . What time will the trains take to cross each other ?

Answer 1

Let length of each train be x meter.

Then, speed of 1^st train = x/18 m/sec;

Speed of 2^nd train = x/12 m/sec;


Now,
When both trains cross each other, time taken =Total Distance /Total Speed

= [2x/{(x/18)+(x/12)}]

== [2x/{(2x/36)+(3x/36)}]

= 2x/[(2x+3x)/36] = 2x*36/5x

= 72/5

= 14.4 seconds.