Multiple choice

A boatman takes his boat upstream from place A to place B, where AB = 21 km. Then, he returns to place A. He takes 10 hours in all. The time taken by him to row 7 km downstream is equal to the time taken by him to row 3 km upstream. (Assume he rows with the same speed upstream as downstream) Which of the following is the ratio of upstream speed to downstream speed?

  1. 3/7

  2. 4/7

  3. 6/7

  4. 2/7

  5. None of the above
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A Correct answer
Explanation

Let upstream speed be U and downstream speed be D. Time taken to row 7 km downstream = 7/D. Time taken to row 3 km upstream = 3/U. Given 7/D = 3/U, so U/D = 3/7.

AI explanation

Because the time taken to row specific distances is equal, the ratio of upstream speed to downstream speed equals the ratio of their respective distances. Therefore, the upstream speed divided by the downstream speed equals 3 divided by 7. This yields the ratio 3/7.

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