Question
Speed of a boat in still water to speed of boat in
upstream is 10:7. If the boat can travel 390 km in downstream in 5 hours, then find the time taken by the boat to cover 18 km in still water.Solution
Let speed of boat in still water and speed of boat in upstream be ‘10x’ km/h and ‘7x’ km/h, respectively. Speed of stream = 10x – 7x = 3x km/h Speed of boat in downstream = 10x + 3x = 13x km/h So, 13x = 390/5 = 78 Or, x = 6 Speed of boat in still water = 10 × 6 = 60 km/h Desired time = 18/60 = 18 minutes
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