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From: jr@bbnccv.UUCP (John Robinson)
Newsgroups: net.puzzle
Subject: 1000 Lockers
Message-ID: <233@bbnccv.UUCP>
Date: Mon, 22-Apr-85 01:32:02 EST
Article-I.D.: bbnccv.233
Posted: Mon Apr 22 01:32:02 1985
Date-Received: Tue, 23-Apr-85 07:20:32 EST
Reply-To: jr@bbnccv.UUCP (John Robinson)
Organization: Bolt Beranek and Newman, Cambridge, MA
Lines: 18

I'm new to this newsgroup.  Hope this isn't a repeat:

Lining the corridor of a school are 1000 lockers.  The first student
to arrive at school one morning decides to open the doors to all 1000
lockers.  The second student to arrive that morning decides to go down
the hall and close the door of every second locker (that is, lockers
2, 4, 6, etc.).  The third student to arrive that morning goes down
the hall and changes the status of every third locker (that is, if the
door is open, she will shut it and if the door is closed, she will
open it).  As the students arrive, this process continues, with the
fourth student affecting lockers 4, 8, 12, etc., and the fifth student
changing the status of lockers 5, 10, etc., until the 1000th student
goes all the way down the hall to change the status of the 1000th
locker.  Now, after all this has been done, which lockers are open,
which are closed, and why?

Enjoy,
/jr