Multiple choice

A man can row a boat at 8 km/h in still water. If the speed of the water current is 2 km/h and it takes him 2 hours to row to a place and come back, then how far off (in km) is the place?

  1. 7.5

  2. 6

  3. 9.5

  4. 10
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A Correct answer
Explanation

Let distance be D. Boat speed = 8, current = 2. Downstream speed = 10, upstream = 6. Time = D/10 + D/6 = 2. (3D + 5D)/30 = 2 -> 8D = 60 -> D = 7.5 km.

AI explanation

Using the formula for total time, we set up the equation D / (8 + 2) + D / (8 - 2) = 2, where D is the distance to the place. This simplifies to D / 10 + D / 6 = 2. Finding a common denominator gives (3D + 5D) / 30 = 2, which results in 8D / 30 = 2. Solving for D yields 16D = 60, so the distance is 7.5 km.

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