Question
A boat can travel 21 km downstream in 42 min. The ratio
of the speed of the boat in still water to the speed of the stream is 5: 1. How much time will the boat take to cover 25 km upstream?Solution
Speed of downstream = D/T = 21 × (60/42) = 30 km/hr The ratio of the speed of the boat in still water to the speed of the stream = 5: 1 (5x, x) => 6x = 30 => x = 5 Speed of upstream = 5x – x = 4x = 20 km/hr Distance = 25 km Time = D/S = 25/20 = 1(1/4) hr
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