The Truth Tree's Math and Logic Board (Popularity: ): Collection of math and logic puzzles ranging in levels of difficulty. IBM Research: Ponder This (Popularity: ): Monthly logic and math puzzles set by IBM researchers with solutions. TechInterview (Popularity: ): Answers to technical interview questions, programming problems, and brain teasers. Perplexus (Popularity: ): A forum and collection of brain teasers, logic problems, math problems, paradoxes, science games, probability, riddles, and geometric shapes. The puzzles are searchable and categorized, ... The Monty Hall Problem (Popularity: ): A probability theory puzzle with solutions. [English and German.] Mathematical Jigsaw Puzzles (Popularity: ): Information on polyominos and square puzzles. WU Forums (Popularity: ): Discussion board hosted at Berkeley with talk about a variety of solved and unsolved brain teasers. Two Envelope Paradox - Solution (Popularity: ): Claims that the two envelope paradox comes from the incorrect use of probabilities. Quick Logic Puzzles (Popularity: ): Use the clues provided to deduce the correct sequence of numbers in the hidden code. The Puzzles of Oscar (Popularity: ): Contains puzzles and games with solutions. Monty Hall Game (Popularity: ): JavaScript example of the Monty Hall Game. This game demonstrates the real (empirical) affect of statistics. [Does not display correctly in all browsers.] Leisure Ideas: Puzzles (Popularity: ): Some mathematical puzzles with answers and/or a hint. CellFighter (Popularity: ): Shareware game based around an extension of the game of life. PuzzlePicnic (Popularity: ): A place to do puzzles and relax, but also a place where puzzle solvers and puzzle makers meet, entertain and challenge one another.