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IMO 1969 - Longlist Problems Question 60

IMO Shortlist · IMO 1969 - Longlist Problems

Question 60

(SWE 3) Find the natural number $n$ with the following properties:

(1) Let $S=\{p_1,p_2,\ldots\}$ be an arbitrary finite set of points in the plane, and $r_j$ the distance from $P_j$ to the origin $O$. We assign to each $P_j$ the closed disk $D_j$ with center $P_j$ and radius $r_j$. Then some $n$ of these disks contain all points of $S$.

(2) $n$ is the smallest integer with the above property.