A train crosses a bridge of length 900 m in 90 sec and crosses a man standing on the bridge in 54 sec. The train is travelling at a uniform speed. Find the length of the train.

Let the length of the train be L metres. Because the train travels at a uniform speed, its speed equals L divided by 54, which also equals (L plus 900) divided by 90. Solving the equation L divided by 54 equals (L plus 900) divided by 90 yields 90L equals 54L plus 48600. Subtracting 54L from 90L gives 36L equals 48600, so L equals 1350 metres.

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