Question

A boy goes to market from his home with speed of 40 km/h and returns back from market to his home along the same path with speed of 10 km/h. The average speed of the boy for the entire journey is

• A. 32 km/h
• B. 16 km/h
• C. 40 km/h
• D. Zero

Answer 1

The correct option is B 16 km/h

Lets consider $x=$ distance between the market and the home

A boy goes to market from home with speed $40km/h$

$t_1=\frac{x}{40}hr$

And return back from the market to home with speed $10km/h$

$t_2=\frac{x}{10}hr$

Average speed of the boy from the entire journey

$v_{avg}=\frac{Totaldistance}{Totaltime}$

$v_{avg}=\frac{x+x}{\frac{x}{40}+\frac{x}{10}}$

$v_{avg}=\frac{2x}{0.125x}$

$v_{avg}=16km/h$

The correct option is B.