The speed of a boat downstream is 15 km/hr and the speed of current is 3 km/hr. Find the total time taken by the boat to cover 15 km upstream and 15 km downstream.

A. 2 hours 40 minutes

B. 2 hours 42 minutes

C. 2 hours 10 minutes

D. 2 hours 30 minutes

Answer: Option A

Solution(By Examveda Team)

Given,
Speed of boat in downstream = 15 km/hr
Speed of current = 3 km/hr
Speed of boat in still water = 12 km/h
Time taken at upstream
$$\eqalign{ & = \frac{{15}}{{12 - 3}} \cr & = \frac{{15}}{9}{\text{hr}} \cr & = 1\,{\text{hour}}\,40\,{\text{minutes}} \cr} $$
Time taken at downstream
$$\eqalign{ & = \frac{{15}}{{12 + 3}} \cr & = \frac{{15}}{{15}}{\text{hr}} \cr & = 1\,{\text{hour}}\, \cr} $$
∴ Total time = 2 hours 40 minutes