### $\text{ D.} \frac{600}{53} \mathrm{~km} / \mathrm{h}$\text { A. } \frac{1600}{53} \mathrm{~km} / \mathrm{h}

Let distance be 120 km Hence 30 km is covered by @25 kmph and 40 km covered by @30 kmph and rest 50 km has been covered @50 kmph Now, $\begin{array}{l}\text{ average }=\Large\frac{120}{\text{ total time taken }}\\ =\Large\frac{120}{\frac{30}{25}+\frac{40}{30}+\frac{50}{50}}\\ =\Large\frac{3600}{106}\\ =\Large\frac{1800}{53}\mathrm{~km}/\mathrm{h}\end{array}$