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Who played first? (Posted on 2004-05-07) Difficulty: 3 of 5
Given this tic-tac-toe position, as played by two expert players, who went first and where? Also, which was the last "move"?
 X | O | O 
---+---+---
   |   | X
---+---+---
   | X | O
(An expert player is a player who would never play in such a way that would allow his opponent to win, and who would also try to get the possible best result.)

  Submitted by e.g.    
Rating: 3.7000 (10 votes)
Solution: (Hide)
Let's number the top cells 1-2-3, the middle cells 4-5-6, and the bottom cells 7-8-9.

If X were to move, he could win by playing at 4 -- and since tic-tac-toe is always a draw between experts players, then it must be O's move, and thus O played first.

If O had started at a corner, X --being a perfect player-- would have answered at the center; thus, O started at 2, and X answered either at 1 or 8. (Answering at 6 would lead to a loss.)

In both cases, the final play for X was at 6.

Comments: ( You must be logged in to post comments.)
  Subject Author Date
Puzzle AnswerK Sengupta2022-06-22 22:30:53
X gamermisao2005-01-10 16:33:15
i don't knowAshley2004-12-26 15:07:41
SolutionNo Subjectnathan2004-09-15 06:24:58
re: Guy SofferPeter2004-05-13 19:01:43
re: solved..i thinkGuy Soffer2004-05-13 03:56:36
re(2): Sum it UpScott2004-05-12 18:02:14
solved..i thinkPeter2004-05-12 16:39:48
Some Thoughtsre: Sum it UpFederico Kereki2004-05-11 21:39:44
SolutionSum it UpScott2004-05-10 15:59:32
SolutionStarting to work...Federico Kereki2004-05-09 21:58:13
re: ionoFederico Kereki2004-05-09 21:49:04
SolutionNo SubjectGuy Soffer2004-05-09 12:57:18
re: The true solution!SilverKnight2004-05-08 18:17:00
SolutionThe true solution!Tristan2004-05-08 13:56:46
solutionA2004-05-08 09:44:21
My guesselson2004-05-08 05:56:38
re: solution - c'mon folksThalamus2004-05-08 01:55:21
Some ThoughtsbogusSteve Royer2004-05-08 00:57:33
Some Thoughtssolutionlogischer Verstand2004-05-08 00:00:47
ionodonnie2004-05-07 22:54:37
iono but maybedonnie2004-05-07 22:50:29
re: No Subject - impossible alsoThalamus2004-05-07 18:03:03
No SubjectAshley2004-05-07 17:52:46
Hints/Tipsfirst step or twoTristan2004-05-07 17:25:25
Some Thoughtsre: No Subject - impossibleThalamus2004-05-07 16:50:08
SolutionNo SubjectSam2004-05-07 16:42:52
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