Multiple choice

A boat rows 36 km of a river towards upstream in 9 hours. How long will it take to cover the same distance downstream, if the speed of current is one-fifth the speed of the boat in still water?

  1. 4 hours

  2. 3 hours

  3. 4.5 hours

  4. 6 hours
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let the boat's speed in still water be 5x km/hr. Then current speed = x km/hr. Upstream speed = 5x - x = 4x km/hr. Distance = 36 km, time = 9 hours, so 4x = 36/9 = 4, giving x = 1. Boat speed = 5 km/hr, current = 1 km/hr. Downstream speed = 5 + 1 = 6 km/hr. Time downstream = 36/6 = 6 hours. Option D is correct.

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