There are 10,000 lockers.
One person opens all the lockers.
The second person closes every 2 doors.
The third person counts every three locker and does the opposite to the locker. (Open/close it.)
The fourth person counts every fourth locker and does the opposite to it.
The fifth person counts every fifth locker and does the opposite and so on.
By the time the 10,000th person gets to the 10,000th lockers, would it be closed or opened?