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Make 15


Go to solution Solved by k-man,

Question

Two players take turns naming numbers from 1 to 9. Players may not name numbers that have already been named. If at any point, three of the numbers named by one of the players adds up to exactly 15, that player wins. If neither player has won after all 9 numbers have been named, the game is declared a tie.

 

Who has the advantage in this game? There is a very clever way of answering this.

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  • Solution

this is a game of tic-tac-toe on a magic square, so if both players play correctly the game will always end in a tie.

 

P.S. I remember this being posted on this forum not that long ago, but couldn't easily find the earlier post

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with 5


e.g.
1st. 5
2nd 1
1st 5, 2 ( 5+2=7...he needs 8)
2nd 1,8 to prevent the 1st player to use it...( 1+8=9... the 2nd player needs 6 )
1st 5,2,6 to block the 15 for the 2nd...( 5+2+6=13... he needs 2)
2nd 1,8,2 blocking the 15 for the 1st.
1st 5,2,6,4 and wins because(5+6+4= 15)
The same will be true for all other numbers choosed by the 2nd. player and the 1st. player will win
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this is a game of tic-tac-toe on a magic square, so if both players play correctly the game will always end in a tie.

 

P.S. I remember this being posted on this forum not that long ago, but couldn't easily find the earlier post

 

Oh whoops. Sorry about that. :/

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