There are 100 doors they are all closed.
A Person walks through these 100 doors 100 times. Each time he toggles some of the doors. ( Toggles - close if open, open if close )
In the first walk, he will toggle all the doors
In the second walk, he will toggle every second door, i.e., 2nd, 4th, 6th, 8th and so on
In the third walk, he will toggle every third door, i.e. 3rd, 6th, 9th and so on,
So after 100th Walk, what all door will be open?