Question 1
Count the total number of parallelograms in the grid below (4 horizontal lines × 4 vertical lines):
+---+---+---+
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+---+---+---+
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+---+---+---+
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+---+---+---+
Choose 2 horizontal lines from 4: C(4,2) = 6, Choose 2 vertical lines from 4: C(4,2) = 6. Total = 6 × 6 = 36