Multiple choice

A man takes twice as long to row a distance against the stream as to row the same distance in favor of the stream. The ratio of the speed of the boat (in still water) and the stream is.

  1. $3 : 1$
  2. $2 : 1$
  3. $5 : 3$
  4. $4 : 7$
  5. $6 : 7$
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A Correct answer
Explanation

Let boat speed in still water = b and stream speed = s. Speed against stream = b - s, speed with stream = b + s. Since time taken against stream is twice the time with stream, we have d/(b-s) = 2 × d/(b+s), which gives b + s = 2(b - s). Solving this gives 3s = b, so the ratio b : s = 3 : 1.

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