Question

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

• A. $25\text{km/hr}$
• B. $24\text{km/hr}$
• C. $50\text{km/hr}$
• D. $5\text{km/hr}$

Answer 1

The correct option is B $24\text{km/hr}$

If the distance travelled is same, then
$\text{average speed}=\frac{2v_1{v}_2}{v_1+v_2}=\frac{2\times 20\times 30}{20+30}$
$=\frac{120}{5}=24\text{km/hr}$