Multiple choice

What is the speed of train x (in km/hr.)? I. The length of train x is twice the train y and speed of train y is 100 m/sec. II. The train x crosses train y in 10 seconds. The length of train x is 100 m.

  1. If statement I alone is sufficient but statement II alone is not sufficient.

  2. If statement II alone is sufficient but statement I alone is not sufficient.

  3. If each statement alone (either I or II) is sufficient.

  4. If statement I and II together are not sufficient.

  5. If both statements together are sufficient, but neither statement alone is sufficient.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Statement I gives: Length of train x = 2 × Length of train y, Speed of train y = 100 m/s. But we need speed of train x in km/h - this requires knowing how they cross or some relation. Statement II gives: Train x crosses train y in 10 seconds, Length of train x = 100m. This gives relative speed if we knew length of train y. Even together: from I, Lx = 2Ly and from II, Lx = 100m, so Ly = 50m. Total distance to cross = 100 + 50 = 150m, time = 10s, so relative speed = 15 m/s. But we don't know if they're moving in same or opposite direction, so we can't determine train x's absolute speed. Answer D (not sufficient) is correct.

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