Sohan covers four trips for same distance. His speed on first trip was 240 km/hr and in each subsequent trip his speed was half of the previous trip. What is the average speed of Sohan for these four trips?
Answer & explanation
Correct answer: option 2
Let the distance covered in each trip is d,
For first trip, time = $\frac{distance}{speed}$
= $\frac{d}{240}$
For second trip, time = $\frac{distance}{speed}$
= $\frac{d}{120}$
For third trip, time = $\frac{distance}{speed}$
= $\frac{d}{60}$
For fourth trip, time = $\frac{distance}{speed}$
= $\frac{d}{30}$
Average speed = $\frac{total\; distance}{total\; time}$
= $\frac{4d}{\frac{d}{240} + \frac{d}{120} + \frac{d}{60} + \frac{d}{30}}$
= $\frac{4d}{\frac{15d}{240}}$
= 64 km/hr