Question

A car travels from A and B at a speed of $20km/hr$ and returns at a speed of $30km/hr$. The average speed of the car for the whole journey is

• A. $25km/hr$
• B. $24km/hr$
• C. $50km/hr$
• D. $5km/hr$

Answer 1

The correct option is B $24km/hr$

Lets consider $X=$ distance between A and B.

A car travels from A to B with speed of $20km/h$ at time,

$t_1=\frac{x}{20}hr$

A car return from B to A with speed $30km/h$ at time $t_2$

$t_2=\frac{x}{30}hr$

Average speed, $v_{avg}=\frac{Totaldistance}{Totaltime}$

$v_{avg}=\frac{2x}{t_1+t_2}=\frac{2x}{\frac{x}{20}+\frac{x}{30}}$

$v_{avg}=\frac{2x}{x/12}$

$v_{avg}=2\times 12$

$v_{avg}=24km/h$

The correct option is B.