Question

Suppose you drive to Delhi $(200km$ away) at $400km/hr$ and return at $200km/hr$. What is yours average speed for the entire trip?

• A. Less than $300km/hr$
• B. More than $300km/hr$
• C. Zero
• D. $300km/hr$

Answer 1

The correct option is A Less than $300km/hr$

Average speed $=\frac{TotalDistance}{TotalTime}$
$=\frac{d_1+d_2}{t_1+t_2}$
$=\frac{200+200}{\frac{200}{400}+\frac{200}{200}}[\because t_1=\frac{d_1}{v_1}$ and $t_2=\frac{d_2}{v_2}]$
$=\frac{400}{\frac{1}{2}+1}$
$=\frac{400}{\frac{1+2}{2}}=\frac{800}{3}=266.66=267km/h$