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PAMO Problem 1: Number of trapezoids satisfying a certain condition

Source: 2021 Pan-African Mathematics Olympiad, Problem 1

May 24, 2021
geometrytrapezoidPAMO

Problem Statement

Let nn be an integer greater than 33. A square of side length nn is divided by lines parallel to each side into n2n^2 squares of length 11. Find the number of convex trapezoids which have vertices among the vertices of the n2n^2 squares of side length 11, have side lengths less than or equal 33 and have area equal to 22 Note: Parallelograms are trapezoids.