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IMO Shortlist 2013, Algebra #2

Source: IMO Shortlist 2013, Algebra #2

July 9, 2014
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Problem Statement

Prove that in any set of 20002000 distinct real numbers there exist two pairs a>ba>b and c>dc>d with aca \neq c or bdb \neq d , such that abcd1<1100000. \left| \frac{a-b}{c-d} - 1 \right|< \frac{1}{100000}.