A 280-metre-long train, travelling at a uniform speed, crosses a platform in 60 seconds and a man standing on the platform in 20 seconds. What is the length of the platform?

Using the formula distance equals speed multiplied by time, let the train length be L and its speed be S. Crossing the man in 20 seconds means L equals 20 times S. Crossing the platform in 60 seconds means L plus the platform length equals 60 times S. Substituting 20 times S for L gives 20 times S plus the platform equals 60 times S, meaning the platform is 40 times S. Since L is 280 m, S is 14 m/s, making the platform 40 times 14, which is 560 metres.

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