Multiple choice

What is the speed (in meters per hour) of a motorboat in still water? Statement I: The motorboat covers 100 km downstream in 10 hours. Statement II: The motorboat covers 60 km in upstream water in 10 hours.

  1. The data in statement I alone is sufficient to answer the question, while the data in statement II alone is not sufficient to answer the question

  2. The data in statement II alone is sufficient to answer the question, while the data in statement I alone is not sufficient to answer the question

  3. The data either in statement I alone or in statement II alone is sufficient to answer the question

  4. The data given in both statements I and II together are not sufficient to answer the question

  5. The data given in both statements I and II together are necessary to answer the question.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Let boat speed = b, current speed = c. Statement I: Downstream, b + c = 100/10 = 10 km/h. This gives one equation with two unknowns, so it's insufficient alone. Statement II: Upstream, b - c = 60/10 = 6 km/h. This also gives one equation with two unknowns, insufficient alone. Combining both: b + c = 10 and b - c = 6. Adding: 2b = 16, so b = 8 km/h. Both statements together are necessary, making E correct. Convert to meters/hour: 8 × 1000 = 8000 m/h.

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