The Locker Puzzle
Suppose you're in a hallway lined with 100 closed lockers. You begin by opening every locker. Then you close every second locker. Then you go to every third locker and open it (if it's closed) or close it (if it's open). Suppose you continue doing this to every nth locker on pass number n. After 100 passes, where you toggle only locker #100, how many lockers are open?
For a better visual : During the 3rd time you open/close(whatever maybe the case) locker number 3,then locker number 6 and so on until locker 99.The 4th time you do the same i.e:4th locker,then 8th locker....and so on.