Puzzle of the Day : 36
Tic-Tac-Toe
The game of Tic-Tac-Toe is played in a large square divided into nine small squares.
[1] Each of two players in turn places his or her mark – usually X or O _ in a small square.
[2] The player who first gets three marks in a horizontal, vertical and diagonal line wins.
[3] A player will always place his or her mark in a line that already contains (a) two of his or her own marks or (b) two of his or her opponent’s marks – giving (a) priority over (b)
Assume that both the players are intelligent enough.
1. Who will win the game, O or X?
2. Which was the sixth mark and at which position?
Source : The great book of Puzzles and Teasers
The 7th mark must be placed in square 5 which is the win situation for both X and O. Hence, the 6th mark must be placed in a line already containing two of the opponents marks. There are two such possibilities – the 6th mark would have been either O in square 7 or X in square 9.
As we know both the players are intelligent enough, the 6th mark could not be O in square 7. Instead, he would have placed O in square 5 and would have won.
Hence, the sixth mark must be X placed in square 9. And the seventh mark will be O. Thus O will win the game.
1. X
2. 8th block by 0
1. X
2. 8th block