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The grid can be filled up using only the numbers $1, 2, 3, 4, 5$ so that each number appears just once in each row, once in each column, and once in each diagonal. Which number goes in the centre square?
If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.
This problem is taken from the UKMT Mathematical Challenges.View the previous week's solution