Multiple choice

A boat covers a certain distance downstream. It comes back in 1.5 hours. If the speed of the stream is 4 km/h, then it covers the distance in 1 hour (downstream). What is the speed of the boat in still water?

  1. 18 km/h

  2. 20 km/h

  3. 22 km/h

  4. 24 km/h

  5. 28 km/h
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let boat speed be B and stream speed be 4. Downstream speed is B+4. Distance = (B+4)*1. Upstream speed is B-4. Time taken for return is 1.5 hours, so Distance = (B-4)*1.5. Equating: B+4 = 1.5B - 6, so 0.5B = 10, B = 20 km/h.

AI explanation

Let the speed of the boat in still water be x km/h, making the downstream speed (x + 4) and the upstream speed (x minus 4). Since the distance is constant, the formula distance = speed multiplied by time gives (x + 4) multiplied by 1 = (x minus 4) multiplied by 1.5. Expanding this equation gives x + 4 = 1.5x minus 6, and solving for x results in 0.5x = 10, so the speed of the boat is 20 km/h.

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