A train with 90 km/hr crosses a bridge in 36 seconds. Another train 100 m shorter crosses the same bridge at 45 km/hr. Find the time taken by the second train to cross the bridge?

Speed of the first train = 90 km/hr = 90 x (5/18) m/sec. = 25 m/sec
Let the length of the train and bridge be L metre.
∴ L = 25 x 36 = 900 m.....(1)
Again Speed of the second train = 45 km/hr = 45 x (5/18) = 25/2 m/sec.
Now, putting the value from eqn. (1) we have
Time taken = (900 - 100) x 2/25 = 800 x 2/25 = 64 sec