IMO Shortlist 1969 problem 60


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2. travnja 2012.
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(SWE 3) Find the natural number n with the following properties:
(1) Let S = \{P_1, P_2, \cdots\} 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.
Izvor: Međunarodna matematička olimpijada, shortlist 1969