Question
Speed of a boat in still water to speed of boat in upstream is 5:4. If the boat can travel 360 km in downstream in 15 hours, then find the time taken by the boat to cover 15 km in still water.
Solution
Let speed of boat in still water and speed of boat in upstream be ‘5x’ km/h and ‘4x’ km/h, respectively. Speed of stream = 5x – 4x = x km/h Speed of boat in downstream = 5x + x = 6x km/h So, 6x = 360/15 Or, x = 4 Speed of boat in still water = 5 × 4 = 20 km/h Desired time = 15/20 x 60 = 45 minutes
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