Multiple choice

The speed of a boat in still water is 10 kmph. If it can travel 26 km downstream and 14 km upstream in the same time, then the speed of the stream is

  1. 2 kmph

  2. 2.5 kmph

  3. 3 kmph

  4. 4 kmph
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let s be the speed of the stream. Downstream speed is 10+s, upstream is 10-s. Time = Distance/Speed. 26/(10+s) = 14/(10-s). 26(10-s) = 14(10+s) => 260 - 26s = 140 + 14s => 120 = 40s => s = 3 kmph.

AI explanation

Let the speed of the stream be y kmph; then the downstream speed is 10 + y and the upstream speed is 10 - y. Since the times are equal, 26 divided by (10 + y) equals 14 divided by (10 - y). Cross-multiplying yields 260 minus 26y equals 140 plus 14y, which simplifies to 120 equals 40y, so y equals 3 kmph.

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