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1. A and B are any two subsets of {1, 2, ... , n-1} such that |A| + |B| > n-1. Prove that one can find a in A and b in B such that a + b = n.
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2. n and d are positive integers such that d divides 2n2. Prove that n2 + d cannot be a square.
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3. ABCDEF is a convex hexagon with all its sides equal. Also A + C + E = B + D + F. Show that A = D, B = E and C = F.
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The original problems are in Hungarian. Many thanks to Péter Dombi for the translation.