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IMO 2022 — Complete Shortlist Question 4

IMO Shortlist · IMO 2022 — Complete Shortlist

Question 4

Let $n \geqslant 3$ be an integer, and let $x_{1}, x_{2}, \ldots, x_{n}$ be real numbers in the interval $[0,1]$. Let $s=x_{1}+x_{2}+\ldots+x_{n}$, and assume that $s \geqslant 3$. Prove that there exist integers $i$ and $j$ with $1 \leqslant i\lt j \leqslant n$ such that

$$
2^{j-i} x_{i} x_{j}\gt 2^{s-3}
$$