MEMO 2010 ekipno problem 4


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28. travnja 2012.
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Let n be a positive integer. A square ABCD is partitioned into n^2 unit squares. Each of them is divided into two triangles by the diagonal parallel to BD. Some of the vertices of the unit squares are colored red in such a way that each of these 2n^2 triangles contains at least one red vertex. Find the least number of red vertices.
Izvor: Srednjoeuropska matematička olimpijada 2010, ekipno natjecanje, problem 4