A boat takes 80 minutes to row 12 km upstream and 60 minutes to row 15 km downstream. How long will it take to row a distance of 36 km in still water?

3 hours

Here is the solution of this question,

Speed of boat upstream = \(\frac{12}{80}\) × 60 = 9 km/hr

Speed of boat downstream = \(\frac{15}{60}\) × 60 = 15 km/hr

Speed of boat in still water = \(\frac{15 + 9}{2}\) = 12 km/hr.

Time taken to row a distance of 36 km = \(\frac{36}{12}\) = 3 hrs.