A train without stoppage travels with an average speed of 65 km/h and with stoppage, it travels with an average speed of 52 km/h. For how many minutes does the train stop on an average per hour?

The distance of 13 km covered by the speed of 65 km/hr in time
$$\eqalign{ & \to \frac{{13}}{{65}} = \frac{1}{5} \times 60 = 12\,{\text{min/hr}} \cr & \cr & {\bf{Alternate}}\,{\bf{solution:}} \cr & \left( {\frac{{{\text{Faster speed}} - {\text{Slower speed}}}}{{{\text{Faster speed}}}} \times 60} \right){\text{min/hr}} \cr & = \frac{{65 - 52}}{{65}} \times 60 \cr & = 12\,{\text{min/hr}} \cr} $$