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1

Part of 2013 Indonesia MO

Problems(1)

Counting parallelograms

Source: Indonesian Mathematical Olympiad 2013 Problem 1

9/5/2013
In a 4×64 \times 6 grid, all edges and diagonals are drawn (see attachment). Determine the number of parallelograms in the grid that uses only the line segments drawn and none of its four angles are right.
geometryparallelogramrectanglecombinatorics unsolvedcombinatoricsElementary counting