Multiple choice

Each of the questions given below consists of a question followed by three statements. You have to study the question and the statements and decide which of the statement(s) is/are necessary to answer the question. What is the speed of the boat in still water? I. The speed downstream is 12 kmph. II. The speed upstream is 4 kmph. III. In a to and fro journey between two points, the average speed of the boat was 6 kmph.

  1. I and II only

  2. All I, II and III

  3. III, and either I or II

  4. Any two of the three

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

Let boat speed be b and stream speed be s. I: b+s = 12. II: b-s = 4. III: Average speed = 2(b+s)(b-s) / (b+s + b-s) = 2(b^2-s^2) / 2b = (b^2-s^2)/b = 6. Any two statements allow solving for b and s.

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