A train 300 m. long is running at a speed of 35 km/hr. Another train 200 m. long is coming from opposite direction at a speed of 25 km/hr.Then what is the time taken by trains to cross each other is?

When two trains cross each other from opposite directions, their relative speed is the sum of their individual speeds. Total distance to be covered is the sum of both train lengths (300 + 200 = 500m). Relative speed = 35 + 25 = 60 km/hr = 60 × 5/18 = 50/3 m/s. Time = Distance/Speed = 500 ÷ (50/3) = 30 seconds. Option A (20 sec) is incorrect - it would require a much higher relative speed.