IMO Shortlist 1970 problem 12
Dodao/la:
arhiva2. travnja 2012. Given
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coplanar points, no three collinear, prove that at most

of the triangles formed by the points have all angles acute.
%V0
Given $100$ coplanar points, no three collinear, prove that at most $70\%$ of the triangles formed by the points have all angles acute.
Izvor: Međunarodna matematička olimpijada, shortlist 1970