This question already has an answer here:
- The security guard problem 1 answer
I am faced with the following problem as homework- a man has 1000 doors. he opens every door, and then he closes every second door. Then he works on every third door- if it's open, then he closes it. if it's closed, he opens it. Then he works on every fourth door, fifth door, and so on all the way until the 1000th door. I need find the amount of doors left open and their numbers (Door 1, Door 2, etc.).
Can someone please tell me the first step to solving this and what kind of mathematics I need to use.