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Problem 20 (2019 AMC 10A)

AMC 10Hard

From module Pigeonhole Principle

Problem

The numbers 1,2,,91,2,\dots,9 are randomly placed into the 99 squares of a 3×33 \times 3 grid. Each square gets one number, and each of the numbers is used once. What is the probability that the sum of the numbers in each row and each column is odd?

Show me the solution

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