Even row and column sums in a 3 by 3 grid
Question
The numbers are placed in a random arrangement in the nine cells of a grid, one number per cell. Find the probability that all three row sums and all three column sums are even.
Short answer
. A row sum is even only when the row contains an even number of odd entries ( or ). Then the total count of odd numbers across the three rows would be even, but contains five odd numbers, so no arrangement works.
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Open the worked solutionLessons behind this question
- Counting and Combinatorics
- Series and the Geometric Series: Partial Sums and Convergence
- Sample Spaces, Events, and the Probability Axioms
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