Question

A man takes 40 minutes to cover a certain distance at the speed of 6km/hr. How much should he increase his speed to cover the same distance in 30 minutes?

Answer 1

$$\begin{gathered} \mathrm{Original}\mathrm{speed}\mathrm{of}\mathrm{man}=6\mathrm{km}/\mathrm{h} \\ \mathrm{Time}\mathrm{taken}\mathrm{by}\mathrm{man}\mathrm{to}\mathrm{cover}\mathrm{a}\mathrm{certain}\mathrm{distance}=40\min =\frac{40}{60}\mathrm{hr}=\frac{2}{3}\mathrm{hr} \\ \mathrm{Now},\mathrm{distance}\mathrm{covered}=\mathrm{speed}\times \mathrm{time}=6\times \frac{2}{3}=4\mathrm{km} \\ \mathrm{Now},\mathrm{man}\mathrm{wants}\mathrm{to}\mathrm{cover}\mathrm{the}\mathrm{distance}\mathrm{in}30\min . \\ \mathrm{So},\mathrm{distance}\mathrm{travelled}=4\mathrm{km} \\ \mathrm{Time}\mathrm{taken}=30\min =\frac{30}{60}\mathrm{hr}=\frac{1}{2}\mathrm{hr} \\ \mathrm{Now},\mathrm{new}\mathrm{speed}=\frac{\mathrm{distance}}{\mathrm{time}}=\frac{4}{1/2}=8\mathrm{km}/\mathrm{h} \\ \mathrm{So},\mathrm{the}\mathrm{man}\mathrm{has}\mathrm{to}\mathrm{increase}\mathrm{his}\mathrm{speed}\mathrm{by}2\mathrm{km}/\mathrm{h}\mathrm{to}\mathrm{cover}\mathrm{the}\mathrm{same}\mathrm{distance}\mathrm{in}30\min . \end{gathered}$$