A man can reach a certain place in 30 hours. If he reduces his speed by $$\frac{1}{15}$$th, he comes 10 km less in that time. Find his speed in km per hour.

$$\eqalign{ & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\text{Actual}}\,\,\,\,\,\,\,\,\,\,\,{\text{Reduced}} \cr & {\text{Ratio of speed}} = {\text{15}}\,\,\,\,\,\,\,\,\,{\text{:}}\,\,\,\,\,\,\,\,\,\,{\text{14}} \cr & {\text{Ratio of time}}\,\,\, = {\text{14}}\,\,\,\,\,\,\,\,\,{\text{:}}\,\,\,\,\,\,\,\,\,{\text{15}} \cr & {\text{14}} \to {\text{28 hrs}} \cr & {\text{15}} \to {\text{30 hrs}} \cr & {\text{So, in 2 hrs it travels 10 kms}} \cr & {\text{Speed = }}\frac{{10}}{2} = 5{\text{ km/hr}} \cr} $$