A man on tour travels first 160 km at 64 km/hr and the next 160 km at 80 km/hr. Find the average speed for first 320 km of tour.

A. 70.11 km/hr

B. 71.11 km/hr

C. 72.11 km/hr

D. 73.11 km/hr

Correct Answer :

B. 71.11 km/hr

We know Time = Distance/speed So total time taken =$\left(\frac{160}{64}+\frac{160}{80}\right)=\frac{9}{2}hr$ Time taken for 320 Km =$320\times \frac{2}{9}=71.11km/hr$