This is a puzzle by John Horton Conway (Eureka October 1959) which was also popularized by Martin Gardner (Scientific American November 1970) .

The diagram is of a flattened dodecahedron. Each face has five edges. There are 12 faces on a dodecahedron, and there are, coincidentally, 12 ways to seat 5 people at a round table (if you don't consider clockwise/counterclockwise to be important). Try to color the dodecahedron (by clicking on the edges) so that each face represents a different "seating arrangement".

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