MathDB
9x9 board

Source: Singapore MO 2011 open round 2 Q2

July 2, 2011
combinatorics proposedcombinatorics

Problem Statement

If 46 squares are colored red in a 9×99\times 9 board, show that there is a 2×22\times 2 block on the board in which at least 3 of the squares are colored red.
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