Multiple choice

Each of given questions consists of a question followed by informations in three statements. You have to study the question and the statements and decide that information in which of the statement(s) is/are necessary to answer the question. find the speed of the man in still water? Statement I: A man can row 25 km upstream and 45 km downstream in 10 hours. Statement II: he can also travel 40 km in upstream and and 55 km downstream in 12 hours. Statement III: the distance travelled by man is same during upstream and downstream movement.

  1. Any two

  2. I and II

  3. I and II or III

  4. Only I

  5. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let boat speed = b, stream speed = s. From I: 25/(b-s) + 45/(b+s) = 10. From II: 40/(b-s) + 55/(b+s) = 12. Let x = 1/(b-s) and y = 1/(b+s). Then 25x + 45y = 10 and 40x + 55y = 12. Solving gives x = 1/10, y = 1/15. So b-s = 10, b+s = 15, giving b = 12.5. Statement III is not needed as the equations from I and II are sufficient.

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