Question

A car travels the first half of a distance between two places at a speed of 30 km/hr and the second half of the distance at 50 km/hr. The average speed of the car for the whole journey is

• A. 42.5 km/hr
• B. 40.0 km/hr
• C. 37.5 km/hr
• D. 35.0 km/hr

Answer 1

The correct option is C

37.5 km/hr

$v_{avg}=\frac{d}{\frac{d}{2v_1}+\frac{d}{2v_2}}$

$=\frac{2v_1{v}_2}{v_1+v_2}$

$=\frac{2\times 30\times 50}{30+50}$

= $\frac{75}{2}$

$=37.5$km/hr