A train is scheduled to cover the distance between two stations 46 km apart in one hour. If it travels 25 km at a speed of 40 km/hr, find the speed for the remaining journey to complete it in the scheduled time :

Time taken to travel 25 km :
$$\eqalign{ & = \left( {\frac{{25}}{{40}}} \right){\text{hr}} \cr & = \frac{5}{8}{\text{ hr}} \cr} $$
Remaining time :
$$\eqalign{ & = \left( {1 - \frac{5}{8}} \right){\text{hr}} \cr & = \frac{3}{8}{\text{ hr}} \cr} $$
∴ Required speed :
$$\eqalign{ & = \left( {21 \times \frac{8}{3}} \right){\text{km/hr}} \cr & = 56{\text{ km/hr}} \cr} $$