For the first time ever, I found myself really excited by ds's homework and even more excited by the answer. I actually did end up understanding how maths can be beautiful.
This was the question: you have a corridor with 1000 doors and 1000 people lining up to walk down the corridor. Person 1 opens all of the doors, person 2 shuts all the doors that are a multiple of 2, person 3 touches all of the doors that are a multiple of 3 and shuts the open ones and opens the closed ones. Person 4 does the same for multiples of 4 and person 5 for multiples of 5 etc. all the way up to person 1000 who shuts the last door.
How many doors are left open after the 1000th person has walked down the corridor?
I loved this question, I really did so I thought I would share it with anyone else out there who likes maths.