The Peg Solitaire Army is a problem spun off from a classic recreation, and yet another example of the golden ratio turning up where you least expect it. If you want to look at the game more deeply, George Bell's solitaire pages are the ne plus ultra: There's more about the solitaire army (and variants), ... [more inside]
The regular polygons have been kidnapped by ninjas. Are you a bad enough dude/tte to construct the regular polygons with nothing but a virtual compass and straightedge? [more inside]
92 years young, the delightful Raymond Smullyan is a mathematician, logician, magician, concert pianist, and Taoist philosopher - who also pioneered retrograde chess problems.
"Gary Foshee, a collector and designer of puzzles from Issaquah near Seattle walked to the lectern to present his talk. It consisted of the following three sentences: "I have two children. One is a boy born on a Tuesday. What is the probability I have two boys?"" [more inside]
Interactive mathematics miscellany and puzzles, including 75 proofs of the Pythagorean Theorem, an interactive column using Java applets, and eye-opening demonstrations. (Actually, much more.)
Maths puzzles and more problems. Found whilst searching for the fiendish the Monty Hall Problem. A Tangled Tale, indeed.
Cut the Knot. Interactive mathematics miscellany and puzzles.
Recreational mathematics and fractal graphics continue to stimulate the mind and foster student interest in mathematics. Some favorite authors & books in this area include: Martin Gardner's books (like The Colossal Book of Mathematics and The Night is Large), Cliff Pickover's books (like The Mathematics of Oz and The Zen of Magic Squares), Calvin Clawson's Mathematical Mysteries, Ian Stewart's books and puzzles, and Ivars Peterson's writings (like Islands of Truth). What are your favorite books and web sites in this area for stretching the mind and eye?
What Color is My Hat? I [heart] these mathematical conundrums -- simple, easy-to-state, seemingly obvious logic problems that have solutions that completely defy common sense. Here's another you can spring on a friend: "You want to fry up three pieces of french toast. You have a frying pan that is just large enough to accomodate two pieces of bread at a time. If it takes you 30 seconds to fry one side of bread, and each piece of must be fried on both sides, how long will it take you to cook up three pieces (assuming that the act of flipping a piece or adding/ removing it to or from the pan takes no time). Think about it. Answer inside.