Multiple choice

A streamer goes downstream from one port to another in 4 hours. It covers the same distance upstream in 5 hours. If the speed of the stream is 2 km/h, then the distance between the two ports is

  1. 80 km

  2. 81 km

  3. 70 km

  4. 71 km
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A Correct answer
Explanation

Let boat speed be B and stream speed be 2. Downstream speed = B+2, Upstream = B-2. Distance = 4(B+2) = 5(B-2). 4B + 8 = 5B - 10. B = 18. Distance = 4(18+2) = 80 km.

AI explanation

Let the speed of the streamer in still water be x km/h. The downstream speed is (x + 2) km/h and the upstream speed is (x - 2) km/h. Since distance is constant, 4(x + 2) equals 5(x - 2). Solving 4x + 8 = 5x - 10 gives x = 18, and the distance is 4(18 + 2), which equals 80 km.

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