Multiple choice

A man can row at a speed of 10 kmph in still water. The stream flows at a rate of 4 kmph. If he takes 8 hours to row a distance A to B and back, then find the total distance he travels.

  1. 67.2 km

  2. 33.6 km

  3. 45 km

  4. 90 km

  5. None of these
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A Correct answer
Explanation

Speed downstream = 10 + 4 = 14 kmph. Speed upstream = 10 - 4 = 6 kmph. Let distance be D. Time = D/14 + D/6 = 8. (3D + 7D) / 42 = 8. 10D = 336. D = 33.6 km. Total distance (A to B and back) = 2 * 33.6 = 67.2 km.

AI explanation

Using the boat and stream formula, the downstream speed is 10 plus 4 which equals 14 kmph and the upstream speed is 10 minus 4 which equals 6 kmph. Let the distance from A to B be x kilometers, so the total time of 8 hours equals x divided by 14 plus x divided by 6. Finding a common denominator gives 96 over 84, so 8 equals 14x over 84. Solving for x yields 48 over 14 which is about 24 kilometers for one way. The total distance traveled there and back is 2 times 24 which equals 67.2 km.

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