### A motorist travels to a place 150 km away at an average speed of 50 km/hr and returns at 30 km/ hr. His average speed for the whole journey in km/hr is.

A. 35 km/hr

B. 37 km/hr

C. 37.5 km/hr

D. 40 km/hr

$\begin{array}{l}\text{ Average speed }\\ =\left(\Large\frac{2xy}{x+y}\right)\mathrm{km}/\mathrm{hr}\\ =\left(\Large\frac{2\times50\times30}{50+30}\right)\mathrm{km}/\mathrm{hr}\\ =37.5\mathrm{~km}/\mathrm{hr}\end{array}$