KöMaL 2021 B5168
Each of the integers 1 to 100 is written on a piece of paper. 16 pieces of paper are selected out of the 100 pieces. Is it certain that there will always be four pieces of paper among the selected ones such that the sum of the numbers on two of them equals the sum of the numbers on the other two?
Official text KöMaL. Quoted with source.
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