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

Let the length of the train be L metres

Speed of first train =  $\frac{3600}{18}xL$ m/hour

Speed of secxond train =  $\frac{3600}{12}xL$ m/hour

When running in opposite directions, relative speed = 200 L + 300 L m/hour

Distance to be covered = L + L = 2L metre

Time taken =  $\frac{2L}{500L}x3600$ sec

                 =14.4 sec