Time taken by train of length l metres to pass a pole or a stationary object of length b metres is the time taken by the train to cover (l+b) metres.

Time taken by train of length 1 metres to pass a pole or a stationary object of length b metres is the time taken by the train to cover (1+b) metres.

Time taken by train of length 1 metres to pass a pole or a standing man or a signal post is equl to the time taken by the train to cover 1 metres.

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.

A train crosses a pole in 12 seconds and a bridge of length 170 metre in 36 seconds. Then the speed of the train is :