Suppose you’re in a hallway 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). Let’s call this action reversing a locker. Continue reversing every nth locker on pass number n. After 100 passes, where you reverse only locker #100, how many lockers are open?Answers are due by 2/30/15 at 12:00 AM.
Email your answers to escholium2015@gmail.com with the subject “2/16/15 Puzzle”. The first correct submission will win a $10 Chipotle gift card.
This puzzle was selected by Abhay Malik.