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The Impossible Puzzle, also named Sum and Product Puzzle is a puzzle called "impossible" because it seems to lack sufficient information for a solution. It was first published in 1969 by Hans Freudenthal,〔Hans Freudenthal, Nieuw Archief Voor Wiskunde, Series 3, Volume 17, 1969, page 152〕 and the name ''Impossible Puzzle'' was coined by Martin Gardner.〔.〕 The puzzle is solvable, though not easily. There exist many similar versions of puzzles. ==Puzzle== ''X and Y are two different integers, greater than 1, with sum less than or equal to 100, with Y greater than X. S and P are two mathematicians; S knows the sum X+Y, P knows the product X *Y, and both are perfect logicians. Both S and P know the information in these two sentences. The following conversation occurs:'' * ''S says "P does not know X and Y."'' * ''P says "Now I know X and Y."'' * ''S says "Now I also know X and Y!"'' ''What are X and Y?'' 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sum and Product Puzzle」の詳細全文を読む スポンサード リンク
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