What is the length of a train? (I) The train crosses a 364 metre long platform in 24 seconds. (II) The train crosses a man standing on the platform in 10 seconds. (III) The speed of the train is 72 km./hr.

For train length problems, we need speed and time to cross a known distance. Statement I gives platform length and crossing time, yielding train length if speed is known. Statement II gives time to cross a person (effectively the train's own length at that speed). Statement III gives speed directly. Any two statements together provide sufficient information: I+II uses relative motion, I+III or II+III use explicit speed.