Question

A boy walks to playground at a distance 5km with constant speed 10km/h and walks back with speed 2.5km/h.what is the average speed for round trip

Answer 1

Hi,

Let t₁ be the time taken in going and t₂ is the time taken in returning.

$$\begin{gathered} t_1=\frac{5}{10}=0.5\mathrm{h} \\ \mathrm{and}\mathit{}{t}_2=\frac{5}{2.5}=2\mathrm{h} \\ \mathrm{Total}\mathrm{time}\mathrm{taken}=t_1+t_2 \\ \mathit{=}0.5+2=2.5\mathrm{h} \\ \mathrm{Average}\mathrm{speed}=\frac{\mathrm{Total}\mathrm{distance}\mathrm{travelled}}{\mathrm{total}\mathrm{time}\mathrm{taken}} \\ \Rightarrow \mathrm{Average}\mathrm{speed}=\frac{5+5}{2.5}=4\mathrm{km}{\mathrm{h}}^{-1} \end{gathered}$$