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Random Tic Tac Toe (Posted on 2025-02-17) Difficulty: 3 of 5
If every move in a game of tic-tac-toe is made at random, spread evenly over the remaining spaces, what is the probability the first player wins, the second player wins, or that there is a tie?

See The Solution Submitted by Charlie    
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Some Thoughts hand counted Ties Comment 2 of 2 |
There are (only?) 126 boards of 5 X and 4 O.  Most of these were likely wins before the last move, but I wanted to see what they looked like.
So I drew them all out.

On 16 boards there are no wins. 
On 36 boards there wins for both X and O.
On 12 boards there a win for O but not X.
On 62 boards there's at least one X win and no O.

So the probability of a tie is 16/126.

Next step will be to undo the boards with 2 wins to decide who won first.



  Posted by Jer on 2025-02-17 14:18:14
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