Question

A train covers the first half of the distance between two states stations at a speed of $40km/h$ and the other half at $60km/h$. Then its average speed is

• A. $50km/h$
• B. $48km/h$
• C. $52km/h$
• D. $100km/h$

Answer 1

Answer: (B)

$48km/h$

Let total distance = $d$
$t_1=\frac{d/2}{40}=\frac{d}{80}and{t}_2=\frac{d/2}{60}=\frac{d}{120}$

Total time $=t=t_1+t_2$

Average speed $\frac{d}{t}=\frac{d}{t_1+t_2}=\frac{d}{\frac{d}{80}+\frac{d}{120}}=\frac{80\times 120}{80+120}=48km/hr$