Question

A car travels from $A$ to $B$ at a speed of $10\text{km/hr}$ and returns at a speed of $30\text{km/hr}$. The average speed of the car for the whole journey is

• A. $15\text{km/hr}$
• B. $20\text{km/hr}$
• C. $25\text{km/hr}$
• D. $30\text{km/hr}$

Answer 1

The correct option is A $15\text{km/hr}$

If the distance travelled is same, then
$\text{average speed}=\frac{2v_1{v}_2}{v_1+v_2}=\frac{2\times 10\times 30}{10+30}$
$=\frac{600}{40}=15\text{km/hr}$