Which information are necessary to answer the questions asked- What is the length of the train? Statement I: If train can cross a platform in 35 second and a pole in 15 sec. Statement II: If the speed of train is 70 kmph. Statement III: If the length of platform is 400 m.

From Statement I: Crossing pole in 15 sec gives L = 15v, and crossing platform in 35 sec gives L + p = 35v. This alone is insufficient (2 equations, 3 unknowns). With Statement II (speed = 70 kmph): convert to m/s, use L = 15v to find length. With Statement III (p = 400 m): substitute into L + 400 = 35v and L = 15v, solve to get L = 300 m. Thus I + (II or III) is sufficient.