Multiple choice

What is the length of the train travelling at uniform speed? Statement I: The train crossed another train of length 400 m moving in opposite direction in 25 seconds. Statement II: The train crossed a bridge of length 750 m in 45 seconds.

  1. If the data in statement I alone is sufficient to answer the question.

  2. If the data in statement II alone is sufficient to answer the question.

  3. If the data either in statement I alone or statement II alone are sufficient to answer the question.

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

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

Statement I: Train crosses 400m train in 25 seconds moving opposite. Relative speed = (L + 400)/25, but we don't know either train's speed. Statement II: Train crosses 750m bridge in 45 seconds. Speed = (L + 750)/45. Even together, we have two unknowns (our train's length L and speed v) but the relationship involves another train's unknown speed. Statement I doesn't give us the other train's speed, so even combining both statements is insufficient to find L.

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