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If the square is completed with the letters A, B, C, D and E so that no row, column or either of the two main diagonals contains the same letter more than once, which letter should replace the asterisk?

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 archive of all weekly problems grouped by curriculum topic*