RSSLinks
Problems and Puzzles
A collection of websites containing problems and puzzles of varying difficulty. Some are purely mathematical, others are of a recreational nature. Be warned that many of the mathematical problems would be considered "4 Star".
Mathematical
- Nick's Puzzles range over geometry, probability, number theory, algebra, calculus, and logic. Problems and solutions are presented clearly and provide an excellent challenge.
http://www.qbyte.org/puzzles/ - Purdue University Problem of the Week.
http://www.math.purdue.edu/pow/ - Canadian Mathematics Competition.
http://cemc.math.uwaterloo.ca/contests/contests.html - The International Mathematical Olympiad's official website.
http://www.imo-official.org/
Recreational
- wu :: riddles, created by William Wu, contains a massive collection of riddles and puzzles. Although solutions are not published, there is a forum where problems can be discussed.
http://www.ocf.berkeley.edu/~wwu/riddles/intro.shtml - For the definitive guide to dissection problems I would refer you to Stewart Coffin's amazing, The Puzzling World of Polyhedral Dissections.
http://www.johnrausch.com/PuzzlingWorld/ - The rec.puzzles archive is an immense collection of categorised puzzles taken from years of newgroup puzzle discussions.
http://rec-puzzles.org/ - The Grey Labyrinth is a superbly produced and presented website, containing a vast collection of puzzles of a lateral and perplexing nature.
http://www.greylabyrinth.com/ - Although a little ambitious in its name, 'The Ultimate Puzzle Site!' provides a good mixture of challenging problems of varying difficulty.
http://www.dse.nl/puzzle/index_us.html