The Sum and Product Puzzle, also known as the Impossible Puzzle because it seems to lack sufficient information for a solution, is a logic puzzle. It was first published in 1969 by Hans Freudenthal,[1][2] and the name Impossible Puzzle was coined by Martin Gardner.[3] The puzzle is solvable, though not easily. There exist many similar puzzles.
^Hans Freudenthal, Nieuw Archief Voor Wiskunde, Series 3, Volume 17, 1969, page 152