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The distance travelled by the train in 16min 30 seconds will be equal to that travelled by sound (20 min – 16 min 30 sec) = 3 min 30 seconds The train travelled 330 × 210 meters in 16 1/2 minutes. ∴ Speed of the train per hour = (330 × 210 × 2 × 60)/(33 ×1000) = 252 km/hr ALTERNATE METHOD: Let speed of train = x m/s The distance covered by bullet with a speed of sound 330m/s in 20 minutes is equal to distance covered by train & bullet together in 16 min 30 sec So let speed of train = x m/s So 330 × 20 = (x+330) × 16 ×1/2 6600 × 2/33 = x + 330 So x + 330 = 400 Or x = 70 m/s = 70 × 18/5 kmph = 252kmph
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