Question
A boat running downstream covers a distance of 50 km in
2(1/2) hrs and the same distance upstream in 10 hrs. What is the speed of the boat in still water?Solution
Let the speed of boat in still water be x km/hr Speed of the stream = y km/hr Now, speed downstream (u) = (x + y) km/hr, and Speed upstream (v) = (x - y) km/hr According to question, Speed downstream = distance/time (x + y) = (50 × 2)/5 (x + y) = 20……………(i) Speed upstream = distance/time (x - y) = 50/10 (x - y) = 5…………………..(ii) Now, speed of boat in still water = (u + v)/2 km/hr ∴ Speed of boat in still water = (20 + 5)/2 km/hr = 25/2 km/hr = 12.5 km/hr
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