Today Puzzle #723
Puzzle No. 723 鈥� Wednesday 22 April
Stephen is playing with his daughters Matilda and Louisa. He taught them to play noughts and crosses and the girls have been playing it all day. Louisa wants to tease her daddy though, and tells him “Daddy, this game ended in a tie with 5 X and 4 O. Three of the corners (up-right, up-left and down-right) have an X. Can you tell what we put in the rest of the square without looking?”
Today’s #PuzzleForToday has been set by Dr Nicos Georgiou, a senior mathematics lecturer from the University of Sussex.
Click here for the answer
In fact, this is possible. The down left corner cannot be an X; there are 5 Xs so no matter where the 5th one would go, it would create a triple and so the game wouldn’t end in a tie. Now, the centre cannot be an X either, because then a diagonal would be full of X and again X would win. Above (middle of top line) and to the right (middle of right column) of the centre we must also have Os for the same reason. So now we found all the Os. The rest are the Xs.
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