A motorboat's speed is in the ratio 36:5 compared to the speed of the water current. If the boat takes 5 hours and 10 minutes to travel downstream, how long will it take to return upstream?

Explanation

Assume the motorboat's speed is 36x km/h and the current's speed is 5x km/h. The downstream speed is (36x + 5x) = 41x km/h, while the upstream speed is (36x - 5x) = 31x km/h. Given the downstream travel time is 5 hours 10 minutes (which is 31/6 hours), the distance traveled downstream is 41x × 31/6 km. The time taken to return upstream is distance divided by upstream speed: (41x × 31/6) ÷ 31x = 41/6 hours, which equals 6 hours and 50 minutes. Therefore, the boat will take 6 hours to come back.