 Investigations in Mathematics  Eric S. Rowland
Openended problems for high school and college students to "approach creatively and in their own way": Pascal's simplices ("What is the generalization of Pascal's triangle?"), Pythagorean triples, regular polygons ("What is the area of a regular polygon
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 Investigations in Projective Geometry  Dwayne Alvis and Wanda Nabors
How threedimensional scenery is reproduced on a twodimensional piece of paper. Construction exercises and a Geometer's Sketchpad file to download.
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 Invitation to MasterMind  Cut the Knot!, Alexander Bogomolny, with Don Greenwell
Mastermind is a game played by a codemaker and a codebreaker. The codemaker selects a code, a sequence of four colors (digits, pegs or other symbols) chosen from a set of six colors (repetitions allowed). The codebreaker will then try to guess the code.
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 iP  Interlocking Puzzles
Purchase hand crafted hardwood interlocking puzzles made with precision from domestic or exotic hardwoods. Altekruse, Burr, Pentominoe, Polyhedra, Rhombic, Stewart Coffin, Tetrahedron, and Wooden Knot puzzles. Order via email.
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 IPNet: Inverse Problems Network  Patricia K. Lamm, Michigan State University
A network for researchers working on inverse and/or illposed problems, inverse methods, and data inversion methods, including applications to tomography, systems identification, nondestructive evaluation and nonlinear evolution equations. IPNet promotes
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 iPracticeMath
Type in your responses to iPracticeMath's online multiplechoice questions, and press the orange "submit" button to check your answers: addition, subtraction, multiplication, division, algebra, "word to number" (interpreting writtenout quantities), and
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 It Can Take a While to Wander Home (Math Chat)  Frank Morgan, MAA Online
Solution to the challenge: How fast do you get home with a random walk on the line? in the plane? in threespace? in nspace? Eric Brahinsky reports that the median number of steps to get home is 24 on the line, about 32 in the plane, and infinite in
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 Iterated Prisoners' Dilemma  Delayaye, Mathieu, Beaufils
A comprehensive source of information on the Iterated Prisoner's Dilemma, and on the representation, study of, and knowledge about cooperation (and evolution of cooperation) between agents. Strategies, references (papers in English and French, bibliography),
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 IUP Annual Mathematics Competition  Gary Stoudt
A mathematics competition for high school students sponsored by Indiana University of Pennsylvania. Topics include algebra, geometry, and trigonometry. Registration forms may be found online, and previous competitions may be downloaded in PDF, PostScript,
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 IXL Learning
IXL provides free online practice, organized by grade levels K8 and aligned to state standards. Choose one math skill from among the hundreds offered, and submit your answer. Respond incorrectly, and click on the "explanation" button to learn more; get
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 Jaap's Scratch Pad  Jaap Scherphuis
Java applets, generators, and solutions for sudoku, Rubik's Cube, "moving pieces" puzzles, permutation puzzles, and more, including sphere symmetries, polyform, Towers of Hanoi, and many lesser known puzzles from this collector. Scherphuis' articles range
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 jackmathsolutions.com  Jack Koenka
Freely download individual chapters of the AP Calculus AB textbook coauthored by Koenka and Roger Allen. Download problem of the week documents, sample test and assignments, notes, worksheets, and other instructional resources. Koenka invites students
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 Jacopo Notarstefano
Interactive visualizations and puzzles: "Turing's sunflower," which connects leaf arrangements and Fibonacci numbers; "HavelHakimi," which presents nodes and their degrees to construct into a graph; "Fourcoloring a Dodecahedron"; and a logic puzzle
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 James Propp
James Propp studies tilings, games, and other aspects of combinatorics, probability, and dynamical systems. Many of his articles are available for download in PostScript and gzipped PostScript formats. Code for C programs related to tilings and cellular
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 janko.at  Angela and Otto Janko
Puzzles, games, and Java applets on logic, number, and chess. See also the Jankos' Retrograde Analysis Corner and analyses of legal moves in chess.
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 JAVA Gallery of Interactive OnLine Geometry  The Geometry Center
Applets illustrating geometry concepts. WebEQ, Hyperbolic Triangles, Lorenz Simulation, OneDimensional Iteration, Tetris, Leap Fractal, Fractals from Iterated Function Systems, Kali: Wallpaper Patterns. Created by The Geometry Center.
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 JavaSketchpad DR3 Gallery  Key Curriculum Press
JavaSketchpad is software that lets you publish sketches from The Geometer's Sketchpad on the Internet. If you have a Javacompatible Web browser, visit this demo gallery for some examples of JavaSketchpad in use: Centroid; Stereo Icosahedron; Hypercube;
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 Jefferson Math Project  Steve Sibol
Resources for integrating Math A and Math B Regents exam questions into the New York State curriculum. PDF, Microsoft Word, and Worksheet Builder versions of exams date back to 1999. See also the JMAP worksheets of Regents questions coordinated with the
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 jensilvermath.com  Jennifer Silverman
Blog by a curriculum designer and the creator of ProRadian radianscale protractors. Posts, which date back to May, 2013, have included "Math Anxiety Relief," "I Love GeoGebra," "Honeycombs and Hot Dogs," "Conic Section Animations," and "O'Beirne Puzzle."
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 Jeremy Kun
Primers, galleries of computer programs and math proofs, and more befitting "a place for elegant solutions." Kun, a mathematics PhD student at the University of Illinois in Chicago with a background in computer science, has also blogged since September,
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 J. Frederic Teubner, The Toymakers of JTEU  J. Frederic Teubner
See, in particular, the Reut·Reut 12x12 Transmagic Square. Also board, card, and dice games, magnets, tshirts, books and tapes, coloring books, an art gallery, and a millennium 2000 computer art calendar.
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 János Bolyai Mathematical Society
A Hungarian mathematical society. Conference information, books published by the society, and problems from the Schweitzer Miklós Mathematical Competition. More information is available in Hungarian.
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 Joe's Number Theory Web  Joe K. Crump
Methods for factoring large numbers, exploration of 2^n mod n, equal sums of like powers, tridigital squares, balanced bases, and Weiferich primes.
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 John Conway's Game of Life  Stephen Stuart
The Game of Life is played on a field of cells, each of which has eight neighbors (adjacent cells). A cell is either occupied (by an organism) or not. The rules for deriving a generation from the previous one are these: Death  If an occupied cell has
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 John Mason's Projects  John Mason
Projects by the author of Thinking Mathematically and former director of the Centre for Mathematics Education: Structured Variation Grids and other animations and applets; studies in algebraic thinking; mathematical explorations; MEMEs (Meaning Enquiry
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 Join the Dots: a Math Line Puzzle  Math Forum
Can you connect 9 dots laid out 3x3 using 4 straight lines, without lifting your pencil from the paper? Questions, hints, solution.
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 Joseph Malkevitch's Home Page  Joseph Malkevitch, York College (CUNYThe City University of New York)
Malkevitch's interests include geometry (polytopes, graph theory, tilings, etc.), discrete mathematics, and mathematical modeling (especially models dealing with fairness and equity issues and codes of all kinds). Most of his research concerns using combinatorial
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 The Josephus Problem  Doug Ensley, Shippensburg University
Explore the problem online, varying the number of people to start and the number to skip: participants arrange themselves in a circle. One is designated number one, and you proceed clockwise, removing e.g. every seventh person. Where should you sit to
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 Josephus Shuffles  Doug Ensley, Shippensburg University
Named for its relationship to the socalled "Josephus Problem," Josephus shuffles mix up a deck of cards in a peculiar way. This interactive page allows you to investigate the final order of the cards for various values of n and k.
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 Joy of Problem Solving  Deepak Kulkarni
Math olympiad programs for elementary and middle school kids by a Ph. D. in computer science and former NASA researcher. See, in particular, the section of Kulkarni's site entitled "How to Work on Problems," which includes essays such as Problem Solving
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 juegosdeingenio.org  Ivan Skvarca
"Un sitio dedicado a los juegos, los acertijos, las paradojas, las diversiones con el lenguaje, los números y las figuras, los ambigramas y todo aquello que maraville y deje perpleja a la inteligencia."
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 JuniorHighMath.com
Free printable worksheets from a middle school teacher: algebra, one variable; algebra with coefficient; twostep algebra with addition; twostep algebra with subtraction; exponents; Pythagorean Theorem; and circles.
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 Juniorszone
A provider of online primary school education offering literacy, numeracy keystage2 strategy based on the UK national curriculum. Areas include e learning, educational games, interactive learning, brain teasers, homework help, and free online tutorials.
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 Just a Usual Day at Unusual School (MegaMath)  Nancy Casey; Los Alamos National Laboratory
Students perform a play that takes place in a school where some of the students always lie and the rest always tell the truth. Terry, the protagonist, is trying to find out which students are which, but at the beginning, there is no way of knowing whom
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 JustMaths  Seager, Christian; Khawaja, Faisal; Muldowney, Melanie
Video tutorials, practice exam questions, and other intervention resources created by three teachers practicing in the UK Midlands. Free resources include "trumps" and exam questions in algebra, data handling, geometry and measure, number, and more. Blog
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 Just Tell Me the Answer  "Never!"  Matt Owen
Blog by an algebra and physics teacher who believes students "have a real chance at understanding if I'm just willing to let them struggle." Posts, which date back to August, 2012, have included "Answering 'the Question,'" "Flipclass Reflections So Far,"
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 K5 Learning  Roy Zanatta
K5 Math and K5 Math Facts are online learning programs for after school study, summer study, and homeschooling. The K5 Math online enrichment program consists of a free math assessment and over a thousand curriculabased, interactive tutorials and quizzes.
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 Kakuro Puzzles  JAKRO Soft LLC
Free printable crossword puzzles that use sums instead of spellings, offered at difficulty levels of easy, medium, hard, and "evil." See also JAKRO's apps and page of tips for solving kakuro.
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 Kalva  John Scholes
Problem sets, with solutions, including a complete set of all International Mathematical Olympiad problems beginning with the first IMO in 1959. The site also includes a large set of Russian Olympiad problems, Putnam problems since 1938, Newman problems,
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 Kamanaga  Madhusudhan Nagarajan
Addition, subtraction, multiplication, and division worksheets to print out or to solve online interactively. Choose adding problems with or without "carrying," subtracting questions with or without "borrowing," and practice dividing with or without remainders.
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 Kangaroo Maths  Kangaroo Maths Ltd
Free maths resources to download in number, algebra, shape and space, and data handling. Assessments include homework sheets and "make the grade" tests; games and puzzles offer World Cup spreadsheet simulations. Kangaroo Maths also hosts Microsoft Word
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 KappAbel  Roald Buvig
Problems from a competition open to pupils in 8th grade in Sweden, Finland (including the Aaland Islands), and Denmark (including Greenland and the Faroe Islands), and ninth graders in Iceland and Norway. See, in particular, the English language weekly
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 Karla Hoffman
A specialist in operations research and combinatorial optimization. Papers in PDF, PostScript, or HTML formats include articles on airline scheduling, set covering, and the traveling salesman problem. Resume and curriculum vitae and syllabus, project,
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 Ka's Geometriepage & MatheGalerie: Grundschulmathematik  Monika Schwarze
Eine Seite zur Grundschulmathematik mit SoftwareTipps. Links zu Mathematikunterrichtseinheiten für Grundschulkinder der Klassen 1 bis Klasse 4; Freiarbeitsmaterialien und kleinen Unterrichtsprojekten. A German Web site for teachers and lovers of geometry,
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 Keep the Traffic Moving!  Dept. of Mathematics, University of Toronto, Canada
Be your own traffic engineer and use this computer simulation to find out how far apart to space the light changes for a given scenario. Includes mathematical models and related questions.
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 Keith's Think Zone  Keith Enevoldsen
Fun math miscellany about number sets, ndimensional hyperspheres and hyperballs, big numbers, areas and volumes, angles — the revolution, shortcut arithmetic, and more. See, in particular, the brain teasers "deadly disease puzzler" and "the world's
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 KenKen  Nextoy, LLC
KenKen is a sudoku variant invented by Japanese mathematics teacher Tetsuya Miyamoto. This site offers puzzles at various levels of difficulty to get you started, as well as rules, tips, news, related products, KenKen programs for your mobile device,
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 Ken Shirriff
A researcher at Sun Microsystems. Annotated bibliographies on fractals and cryptography, and related papers, which may be downloaded in PostScript format. Graphics of Voronoi fractals (dividing the plane into regions closest to a given point) and fractals
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 Ken's Puzzle of the Week  Ken Duisenberg
A weekly puzzle for advanced high school or college level, with a math, geometry, or game focus. The problems are easy to understand but tricky to solve. An archive of previous problems and solutions is included, together with a list of other puzzle sites
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 Key Curriculum Press
Publisher of innovative texts and software applications for teaching mathematics including the Geometer's Sketchpad (dynamic geometry), Fathom (dynamic statistics), TinkerPlots (dynamic data exploration and analysis), Michael Serra's textbook Discovering
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