91st Kürschák Competition 1991

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1.  a >= 1, b >= 1 and c > 0 are reals and n is a positive integer. Show that ( (ab + c)n - c) <= an ( (b + c)n - c).
2.  ABC is a face of a convex irregular triangular prism (the triangular faces are not necessarily congruent or parallel). The diagonals of the quadrilateral face opposite A meet at A'. The points B' and C' are defined similarly. Show that the lines AA', BB' and CC' are concurrent.

3.  There are 998 red points in the plane, no three collinear. What is the smallest k for which we can always choose k blue points such that each triangle with red vertices has a blue point inside?

The original problems are in Hungarian. Many thanks to Carlos di Fiore for supplying an English translation for 1990-1993.

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(C) John Scholes
jscholes@kalva.demon.co.uk
10 Feb 2003
Last corrected/updated 19 Apr 2003