Multiple choice

A boat covers a distance of 24 km against the stream and 36 km down the stream in 6 hours. The same boat covers a distance of 36 km against the stream and 24 km down the stream in 6 hours and 30 minutes, then the time required to cover a distance of 1080 km in still water by boat is

  1. 90 hours

  2. 135 hours

  3. 270 hours

  4. 108 hours
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let b = boat speed in still water, s = stream speed. Downstream speed = b + s, upstream speed = b - s. First trip: 24/(b-s) + 36/(b+s) = 6. Second trip: 36/(b-s) + 24/(b+s) = 6.5. Solving these gives b = 10 km/h, s = 2 km/h. Time for 1080 km in still water = 1080 / 10 = 108 hours. Option D is correct.

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