Question

A man walks on a straight road from his home to a market 2.5 km away with a speed of 5 km/h. Finding the market closed, he instantly turns and walks back home with a speed of 7.5 km/h. If the total time of travel is 40 min find the average speed of the man for the whole journey.

• A. 5 km/h
• B. $\frac{25}{4}$ km/h
• C. $\frac{30}{4}$ km/h
• D. $\frac{45}{8}$ km/h

Answer 1

The correct option is D

$\frac{45}{8}$ km/h

From home to market, the time taken is time = $\frac{d}{v}=\frac{2.5}{5}=\frac{1}{2}$hr $=30$ min.

He returns back with speed of 7.5 km/h in rest of time, that is, 10 minutes.

Distance = $7.5\times \frac{10}{60}=1.25km$

Average speed = $\frac{Totaldistance}{Totaltime}$

= $\frac{(2.5+1.25)km}{\left(\frac{40}{60}\right)hr}$

$=\frac{45}{8}$km/hr.