MathDB
19x19 block of 2013x2013 board has at least 21 marked sqrs

Source: Turkey TST 2013 - Day 1 - P2

April 2, 2013
geometryrectangleinductioncombinatorics proposedcombinatorics

Problem Statement

We put pebbles on some unit squares of a 2013×20132013 \times 2013 chessboard such that every unit square contains at most one pebble. Determine the minimum number of pebbles on the chessboard, if each 19×1919\times 19 square formed by unit squares contains at least 2121 pebbles.
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