Q. A boy walks to his school at a distance of 6$km$ with constant speed of 2.5 $km/hour$ and walks back with a constant speed of 4 $km/hr$. His average speed for round trip expressed in $km/hour,$ is
A) $24/13$
B) $40/13$
C) $3$
D) $1/2$
Explanation
(b) Distance average speed $= \frac{2v_{1}v_{2}}{v_{1} + v_{2}} = \frac{2 \times 2.5 \times 4}{2.5 + 4}$
$= \frac{200}{65} = \frac{40}{13}km/hr$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.