A man takes 100 minutes to cover a certain distance at a speed of 6 km/hr. If he walks with a speed of 10 km/hr, he covers the same distance in :

$$\eqalign{ & {\text{Distance}} = {\text{Speed}} \times {\text{Time}} \cr & {\text{Distance}} = \left( {6 \times \frac{{100}}{{60}}} \right){\text{km}} \cr & {\text{Distance}} = 10{\text{ km}} \cr} $$
$$\eqalign{ & \therefore {\text{ Required time}} = \frac{{{\text{Distance}}}}{{{\text{Speed}}}} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \frac{10}{{10}}{\text{ hrs}} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = {\text{1 hr}} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = {\text{60 min}} \cr} $$