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Problem A. 476. (March 2009)

A. 476. Let n\ge3 be an odd integer, and let A={0,1,...,n-1} denote the set of residual classes modulo n. Call a non-empty subset B\subsetA a Dutch set, if for every a\inA and for every b\inB at least one of b+a and b-a lies in B. Determine the smallest possible cardinality of a Dutch set in terms of n.

Proposed by: Gerhard Woeginger, Amsterdam

(5 pont)

Deadline expired on April 15, 2009.


13 students sent a solution.
5 points:Backhausz Tibor, Blázsik Zoltán, Bodor Bertalan, Éles András, Frankl Nóra, Nagy 235 János, Nagy 314 Dániel, Nagy 648 Donát, Tomon István, Weisz Ágoston, Wolosz János.
4 points:Tossenberger Anna, Varga 171 László.

Problems in Mathematics of KöMaL, March 2009