If two train of length a metres and b metres are moving in opposite direction at u m/s and v m/s: then time taken by trains to cross each other.

If two trains of length a metres and n metres are moving in the same direction at u m/s and vm/s: then time taken by faster train to cross the slower train.

The length of Lucknow mail is 120 m and that of Punjab mail is 80 m These two trains are runing in the opposite direction with velocities of 40 km/h and 50 km/h respectively.The time taken by them to cross each other is:

A train A which is 120 m long is running with velocity 20 m/s while train B which is 130 m long is running in opposite direction with velocity 30 m/s. What is the time taken by train B to cross the train A?