Multiple choice

The speed of a boat is 4 km/hr in still water and the speed of the stream is 2 km/hr. If the boat takes 4 hours to go to a place and come back, then the distance of the place from the starting point is

  1. 6 km

  2. 5 km

  3. 7 km

  4. 8 km

  5. None of these
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A Correct answer
Explanation

Downstream speed = 4+2 = 6 km/hr. Upstream speed = 4-2 = 2 km/hr. Let distance be d. d/6 + d/2 = 4. (d + 3d) / 6 = 4 => 4d = 24 => d = 6 km.

AI explanation

The downstream speed is the sum of the boat's speed in still water and the stream's speed, giving 6 km/hr, while the upstream speed is their difference, giving 2 km/hr. Let the one-way distance be x kilometres; the total time for the round trip is (x divided by 6) plus (x divided by 2), which equals 4 hours. Solving the equation x plus 3x divided by 6 equals 4 yields 4x equals 24, so x equals 6 km.

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