The following questions are accompanied by three statements. You have to determine which statement(s) is/are/sufficient/necessary to answer the question? In what time two trains will cross a 400m long platform? A Trains are running in opposite directions and their speeds are 72km/h and 81km/h respectively. B The length of trains are 180 m. and 210 m. and they reach at the ends of platform simultaneously. C The trains will cross each other in 9 seconds.

We need relative motion information and platform length. A gives speeds in opposite direction (relative speed = 72+81 = 153 km/h = 42.5 m/s). B gives train lengths. C says trains cross each other in 9 seconds, which gives relative speed = (180+210)/9 ≈ 43.33 m/s - inconsistent with A! With A+B: relative speed from A, combined length from B, we can find time to cross platform if we know platform length. But we don't! With B+C: we can verify relative speed, but still need platform length. None of the combinations give us platform length or which train reaches first. So E (None of these) is correct.