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The time taken by a boat to cover a certain distance in still water is 20% less than the time it takes to cover the same distance upstream. The speed of the stream is 4.5 km/h. How much total time…

Question and options

The time taken by a boat to cover a certain distance in still water is 20% less than the time it takes to cover the same distance upstream. The speed of the stream is 4.5 km/h. How much total time (in hours) will the boat take to cover 60 km downstream and 30 km upstream?
  1. 4134\frac{1}{3}
  2. 3893\frac{8}{9}
  3. 4164\frac{1}{6}
  4. 3133\frac{1}{3}

Answer and explanation

Correct answer: B - \(3\frac{8}{9}\)
Still-water time = 0.8 x upstream time means b - 4.5 = 0.8b, so b = 22.5 km/h; downstream 27, upstream 18. Time = 60/27 + 30/18 = 20/9 + 5/3 = 35/9 = 3 8/9 h.

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