On a station a train is stopped for 6 minutes but after this its speed is increased by 4 km hr When ...........

Quant (SSC) Problems on trains

On a station, a train is stopped for 6 minutes, but after this its speed is increased by 4 km/hr. When the train covers 36 km it manages its delay. What is the initial speed of the train?

32 km/h

36 km/h

40 km/h

42 km/h

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Explanation:

Let the speed of train be x km/hr,
36 + x/4 + 6 mins = 36/x
⇒ 36/x - 36/x + 4 = 6/60
⇒ 36 (1/x - 1/x + 4) = 6/60
⇒ 36 (x + 4 - x / x²+ 4x)
⇒ 360 × 4 = x² + 4x
⇒ x² + 4x – 1440 = 0
⇒ x² + 40x – 36x – 1440 = 0
⇒ x(x + 40) – 36(x + 40) = 0
⇒ (x + 40) (x – 36) = 0
⇒ x = 36 km/hr