ITOT 43 Spring 2022 - THPT O - additive practice Question 4

Alice and Bob independently tile a $20\times21$ board with $1\times3$ or $3\times1$ trominoes. They then compare their tilings, and Alice pays Bob one dollar for each tromino occupying exactly the same cells in both tilings. What is the largest amount Bob can guarantee? (5 points)



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