A train covers a distance in 30 minutes. If it runs at 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 minutes is:

Solution (By Examveda Team)

$$\eqalign{ & {\text{Distance}} = 5a \times \frac{1}{2} = 27{\text{ km}} \cr & {\text{Time}} = 20{\text{ min}} = \frac{1}{3}{\text{ hr}} \cr & {\text{Speed}} = \frac{{27}}{{\frac{1}{3}}} = 81{\text{ km/hr}} \cr} $$