A train covers a distance in 30 min if it runs a speed of 54 km/h on an average. The speed at which the train must run to reduce the time of the journey to 20 min is:

none of these 81 km/h 60 km/h 75 km/h

81 km/h

Distance = Speed × Time = 54 × \(\frac{30}{60}\) = 27 km Speed to cover 27km in 20 min. Speed = \(\frac{Distance }{Time }\) = \(\frac{27 × 60  }{20 }\) = 81 km/h