There is a wall with 1000 closed lockers on it. A person walks down the hall opening every other locker. Then the next person opens every 3rd locker. The next opens every fourth locker. The next every fifth locker.

Once this has been done, how many lockers are still closed?

My guess is 93. I counted 2, and then 2 times the primes from 2*7, 2*11, 2*13, to 2*499. I hope I counted right.

Posted by cges on 2002-12-06 19:45:24