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Even row and column sums in a 3 by 3 grid

Question

The numbers 1,2,…,91,2,\dots,9 are placed in a random arrangement in the nine cells of a 3×33\times3 grid, one number per cell. Find the probability that all three row sums and all three column sums are even.

Short answer

00. A row sum is even only when the row contains an even number of odd entries (00 or 22). Then the total count of odd numbers across the three rows would be even, but 1,…,91,\dots,9 contains five odd numbers, so no arrangement works.

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