Multiple choice

Directions: The following question is accompanied by statements A, B and C. You have to determine which of the statements is/are sufficient/necessary to answer the question. What is the ratio between the speed of water current and that of Ameera's boat, respectively? A. Ameera's boat running upstream takes 7 hours 38 minutes to cover a certain distance. B. It takes 2 hours to cover the same distance running downstream. C. There is one more boat travelling upstream at a speed of 21 km/hr.

  1. A and B together are sufficient.

  2. Only B is sufficient.

  3. Only A and C are sufficient.

  4. B and C are sufficient.

  5. All of them are necessary.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let boat speed be B and current speed be C. Statement A gives B-C. Statement B gives B+C. With both, we have a system of two equations with two variables, allowing us to solve for B and C and thus their ratio. Statement C is irrelevant as it describes a different boat.

AI explanation

Let the speed of the boat be b and the speed of the water current be w; we need to find the ratio w divided by b. The distance covered is constant, so the distance equals upstream speed multiplied by upstream time, and also equals downstream speed multiplied by downstream time. From statements A and B, we can set up the equation (b minus w) multiplied by 7.633 hours equals (b plus w) multiplied by 2 hours; dividing both sides by (b plus w) and by 7.633 gives the exact ratio of (b minus w) to (b plus w), which can be solved to find w divided by b. Statement C gives the speed of another unrelated boat, which is irrelevant, so only A and B together are sufficient.

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