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:

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