ஒரு ரயிலானது 90 மீ நீளமுள்ள நடைமேடையில் நின்று கொண்டிருக்கும் ஒரு மனிதரை 15 நொடிகளில் கடக்கிறது. அதேபோன்று நடைமேடையை 30 நொடிகளில் கடக்கிறது. எனில் ரயிலின் வேகம் என்ன? A train crosses a man standing on a 90m-long pavement in 15 seconds. Similarly crossing the stage in 30 seconds. What is the speed of the train?

Let the length of the train be L meters. When the train crosses the man, its speed equals L divided by 15 seconds. When crossing the 90 m platform, the total distance is L plus 90, so the speed also equals (L plus 90) divided by 30 seconds. Equating the two expressions for speed gives L divided by 15 equals (L plus 90) divided by 30. Solving this equation yields 2L equals L plus 90, making the length of the train 90 m and its speed 6 m/s. Converting 6 m/s to km/h by multiplying by 18/5 gives a speed of 21.6 km/hr.

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