Combinatorics · Invariants · Parity · Optimization · Information and questions
On each of \(n > 4\) cards, one of the numbers \(+1\) and \(-1\) is written. A single question consists of naming exactly three of the cards, after which we are told the product of the numbers written on those three cards.
What is the smallest number of questions with which we can always determine the product of the numbers written on all \(n\) cards?
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Serbian Regional Competition 2012, high school grade I, category A, problem 5. Organized by the Mathematical Society of Serbia (DMS). Source