1. Suppose you’re in a hallway lined with 100 closed lockers
2. Begin by opening all 100 lockers.
3. Close every second locker.
4. Go to every third locker and close it if it is open, or open it if it is closed (call this toggling the locker).
5. Continue toggling every nth locker on pass number n.
6. Stop on your hundredth pass of the hallway when you will toggle only locker number 100.
How many lockers are open?