## College Physics (7th Edition)

Average speed, $\bar{s}=88.43 \,\mathrm{km/h}$
Time taken by the motorist to travel 80km - \begin{align*} t_1=\frac{d_1}{s_1}=\frac{80}{100}=0.8\,\mathrm{h} \end{align*} Time taken by the motorist to travel 50km - \begin{align*} t_2=\frac{d_2}{s_2}=\frac{50}{75}=0.67\,\mathrm{h} \end{align*}Total time, $t=1.47\,\mathrm{h}$ Total disatnce, $d=130\,\mathrm{km}$ Average speed - \begin{align*} \bar{s}&=\frac{d}{t}=\frac{130}{1.47}\\&=88.43\,\mathrm{km/h} \end{align*}