Multiple choice

A train running at a certain speed crosses a 300 m and 240 m long bridges in 21 seconds and 18 seconds respectively. What is the speed of the train?

  1. 72 km/hr

  2. 68 km/hr

  3. 65 km/hr

  4. 60 km/hr

  5. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let train length = L meters and speed = S m/s. Crossing bridge means L + bridge_length = S × time. So: L + 300 = 21S and L + 240 = 18S. Subtract: 60 = 3S, so S = 20 m/s = 20 × (18/5) = 72 km/hr. Option A (72 km/hr) is correct. The train length is L = 21×20 - 300 = 120 m, which checks out.

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