 On the Horizon (OTH)  School of Education, University of North Carolina (UNC)
OTH Online: the electronic version of the print publication, with the full text of prior volume years. Also the HORIZON mailing list, seminars and workshops, conferences, and presentations to explore and extend the educational community's thinking about
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 On This Day in Math  Pat Ballew
Mathematically significant events, births, deaths, and more, posted every calendar day. Ballew's blog reveals his thoughts on teaching math. His links and explanations written using The Geometer's Sketchpad include triangle medians; angle bisectors in
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 OOG: the Object Orientation Game  MCM Productions
MCM Productions' first publicly released software application. This 4in1 tiling puzzle game for the MSWindows environment allows players to test their problem solving ability with over 300 puzzles, including Tangrams, Pentominoes, Hexagons and Polyominoes.
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 .oO worksheeps  Felix Heckert
Generate worksheets of customized math exercises, complete with solutions: basic operations with integers, negatives, and fractions; binomial and quadratic formulas; partial roots; percent calculation; curve sketching; metric; derivations; antiderivatives;
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 Open Directory  Science: Math  Netscape
A comprehensive directory of math sites on the Web, listing links of mathematical interest by general topics, math topic, and site name.
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 OpenEnded Assessment in Math  Cooney, Thomas J.; Sanchez, Wendy B.; Leatham, Keith; and Mewborn, Denise S.
Over 450 openended, fieldtested assessment items, distributed more or less equally among elementary, middle school, and high school grade levels. The questions relate to five major content areas, based on the NCTM Standards: number and operation; probability
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 OpenEnded Math Problems  Gwenn Holtz and Mary Lee Malen, Levering School and the Franklin Institute
An eightmonth slate of openended problems for middle school students to solve in preparation for standardized testing. The authors have composed and selected problems that lend themselves to multiple solution paths, and then organized them into three
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 Open Middle  Johnson, Nanette; and Kaplinsky, Robert
"Open middle" problems, hints, and answers, all aligned to the Common Core State Standards (CCSS). Introduced by Dan Meyer, these kinds of math challenges have a "closed beginning," meaning that they all start with the same initial problem; a "closed
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 Optical Data School Media
A publisher of math and science programs, including Windows on Math, an activitybased laserdisc and videotape curriculum built around the NCTM standards. Most products are for levels K8. Find Correlations for Optical Data products to a wide range of
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 Optical Illusions (SandlotScience.com)  SandlotScience
Interactive explorations of optical effects, illusions, distortions, animations, artwork, stories, PDF projects, games, and more. Impossible objects include columns, an endless staircase and animated stairs, Java triangle models, an interlaced tribar,
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 Oranges Project Page  Debbie Lewis; The Levering School, Philadelphia, PA
An eighth grade project. Students use measurement to investigate the proportional relationship between the edible part of an orange and the peel or inedible part of a orange. They investigate different types of oranges such as navel, blood, and clementines
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 Orbifold Pinball  Yevgeniy Dodis; The Geometry Center
A game in which you roll a ball on an unusual playing field. The game board is like ordinary pinball in that it features 'bumpers' off which the ball can bounce. But in this game, the board is 'curved' in such a way that a ball barely missing the bumper
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 The Orbifold Shop (Geometry and the Imagination)  Conway, Doyle, Gilman, Thurston; The Geometry Center
A symmetry project: the Orbifold Shop offers a free coupon for $2.00 worth of parts, installation included, to anyone acquiring a new orbifold. There are only a few kinds of features for twodimensional orbifolds, but they can be used in combinations:
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 Orbit Research
Developers and manufacturers of Orion Talking Scientific calculators the TI84 Plus and the TI36X, the iBill Talking Banknote Identifier, and other "products that enable an independent lifestyle for the physically challenged"  the visually impaired
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 Orbits and Gravitation  MacTutor Math History Archives
A hypertext essay covering Copernicus through Poincaré, LeviCivita, and Birkhoff, with References.
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 Order of Operations  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about order of operations, such as "What is PEMDAS?" and the place of factorials in arithmetic operations.
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 Order of Operations  Math Forum, Ask Dr. Math FAQ
What is the correct order of operations? Why use it? What is PEMDAS?
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 Order Of Operations (SMILE)  Bernice E. Holloway, Bellwood School District 88
A lesson designed to teach students to use grouping symbols and the standard order of operations to simplify numerical expressions; to use the order of operations to evaluate variable expressions; and to use the calculator and computer to solve numerical
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 Origami Page  Joseph Wu
Origami is the art of paper folding. The word is Japanese, literally meaning "to fold" (oru) "paper" (kami). Links to photo galleries, information on origami, files and diagrams, other origami home pages, and areas related to origami (A paper on Molecular
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 Origami Snowflake Game  Rick Nordal
Origami designs to fold from a "snowflake" base — a square of 32 identical 45°45°90° triangles. Topics from Nordal's sixteen chapters include "Base fold geometric snowflakes," "Lightning folds," "How to fold 3 geometric snowflake shapes,"
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 OrigamiUSA
Resources for origami enthusiasts and for those just learning the art of paper folding: Events (calendar, convention, and exhibit information); Resources (model index, links, email discussion list, folding groups directory, and lending library); Shopping
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 Original Lesson Plans  Mathematics  Thirteen/WNET New York
Original Webbased activities developed by Thirteen Ed Online Master Teachers. Each lesson consists of an overview with learning objectives, procedures for teachers, and "organizers" for students  handouts, bibliographies, and other materials. Math
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 Orlando Sessions on Constructivism  The Math Forum
The 1996 AMS/MAA Joint Mathematics Meetings in Orlando, Florida featured presentations on constructivism. The goal: to disseminate innovative, successfully classtested pedagogical theoretical view of how mathematics is learned.
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 ostermiller.org  Stephen Ostermiller
Converters, Calculators, and JavaScript include Multiplication Game, in which letters represent digits in a multiplication problem; Length, which converts between units of length and distance; Roman Numerals, which converts between Arabic and Roman numerals;
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 Ostrich Llama Count  Examining Solution Methods  Suzanne Alejandre
Activity, alignments, directions, extensions, and activity sheets that detail five ways to solve the Problem of the Week (PoW) "Ostrich Llama Count." Originally published in the March, 2013, issue of the CMC ComMuniCator, journal of the California Mathematics
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 Our Town (The Weather Unit: Math Application)  Collaborative Lesson Archive
A lesson that uses and/or introduces new tools in geography, math, and science to make observations and draw conclusions on the local temperature variations in your area. Colorado State Standard addressd: Students use algebraic methods to explore, model,
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 Outposts, the Geometry Forum Newsletter Online  Sarah Seastone; The Math Forum
The newsletter of The Geometry Forum, published in 199495: Swarthmore College's electronic home for geometers of all kinds.
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 Overthinking My Teaching  Christopher Danielson
Blog by a community college math teacher "interested in hard questions about teaching." Posts, which date back to July, 2009, have included "Wump hats," "An unnoticed rule for number language," "The end of word problems," "Cubeyness," "Cardinal and ordinal
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 An overview of Babylonian mathematics  MacTutor Math History Archives
Linked essay exploring the arithmetic and geometry of the Babylonians, who lived in Mesopotamia, a fertile plain between the Tigris and Euphrates rivers. The Babylonian civilization replaced the Sumerian civilisation and the Akkadian civilisation; this
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 An overview of Egyptian mathematics  MacTutor Math History Archives
Linked essay on the development of the Egyptian number systems, and the arithmetical methods they devised to work with their numerals. With references and other related web sites.
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 An overview of Indian mathematics  MacTutor Math History Archives
Linked essay on the contributions of Indian mathematics, in particular the number system invented by the Indians, on which much of mathematical development has rested. With references and other related web sites.
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 Overview of the History of Mathematics  MacTutor Math History Archives
Linked overview from the Babylonians through topics from the twentieth century, with additional sections on notation and communication, brilliant discoveries, how we view history, and a challenge, as well as a 700item general bibliography.
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 Oxford University Press
The world's largest university press, publishing 3,000 new books a year, including scholarly works in all academic disciplines, bibles, music, school and college textbooks, children's books, materials for teaching English as a second language, business
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 P2S Games  P2S Information Systems Pvt. Ltd
Online games that challenge you to click your way to filling containers of liquids (Fill It Up), completing equations with operations (Equation), adding adjacent tiles to maximize their overall sum (Maximize), selecting operations between the 4s to make
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 Packing Videotapes  NASA Lewis Learning Technologies Project
Roger had to pack videotapes 10 to a box. If he had 178 tapes of one kind and 121 of another kind, how many boxes would he need in order to pack them all and not mix the different types? A detailed answer is provided. From NASA's 9th Grade Math Proficiency
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 Page of Conversion (Convert It)  Ramsviks, Adler
Enter a number and press the tab key to convert among bases, tempreatures, and measures and weight.
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 Pages Mathématiques  Lycée de Vienne SaintRomainEnGal (académie Grenoble)
Une série de cours de mathématiques: Géométrie du triangle; Transformations; Géométrie des cercles; Barycentres; Coniques et courbes; Solides; Statistiques; Fractales; Géométrie non euclidienne;
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 Pairing Like Students for Perseverance in Problem Solving  Marie Hogan
Article about how one particular duo of eighth grade PreAlgebra students, paired by ability level, overcame a contentious start to work together and "reach new heights of problemsolving proficiency." Originally published in the March, 2013, issue of
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 Palindromic Numbers and Other Recreational Topics  Patrick De Geest
Many odd facts about big (and little) numbers, including circular primes and palindromic triangulars, tetrahedrals, squares, cubes, and primes. Also assorted odd puzzles, etc.
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 Palindromic Primes  Ivars Peterson (MathTrek)
Palindromic primes are whole numbers, evenly divisible only by themselves and 1, that also have the same sequence of digits read forward or backward... The current record for the largest known palindromic prime is held by Harvey Dubner, a retired electrical
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 Panamath  Panamath.org
Have you ever tried to guess how many jelly beans are in a jar without counting? The Panamath test measures your number sense  your intuitive recognition of numbers and their relationships  and approximate number system (ANS) aptitude. Practice estimating
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 Panitz cooperative learning and WAC web page and much more  Ted Panitz, Cape Cod Community College
Workshops, articles, and other resources on cooperative learning and pedagogy.
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 Pantagraph (Manipula Math)  International Education Software (IES)
A pantograph is a drawing instrument for magnifying figures. Using the applet on this page, by moving the red point to trace an original figure you can automatically obtain a magnified figure with the pen at the blue point.
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 Panthera's Puzzle Contest  Dr. Amy Galitzer; Puzzle University
A weekly contest of math, logic, and word puzzles sponsored by the American Mathematical Society and the University of Maryland Mathematics Department. You can submit your own puzzle for the next contest by signing up to participate, or simply read the
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 paperfolding.com  Eric Andersen
Learn to fold origami from diagrams; read about the history of paperfolding, including the origin of the term "origami." The origami & math essay contains sections such as Origami, Geometry, and the Kawasaki Theorem; and Origami and Topology.
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 PaperFoldingFractals  Joel Castellanos, Rice University
A classroom teaching or personal learning software tool for Windows that can be an introductory lesson to fractals. Simple, stepbystep processes of paper folding can give rise to infinite verities of fractals. The user learns what fractals are and how
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 Paperforms: Polyhedrons for the Masses  John T. Vonachen
Geometric paper sculptures offered for sale.
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 Paperkit
Generate the exact type grid paper using this printable graph paper template. Specify format, units, spacing, margin, and stroke width and color.
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 Paper Models of Polyhedra  Gijs Korthals Altes
Dozens of paper models of polyhedra: Platonic and Archimedean solids, compounds, caleidocyli, and more. Print the images, cut, and glue them together, or download the models in zipped CorelDraw or GIF format.
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 Paper Mosaics  Alex Bateman
Origami tessellations consist of a simple crease pattern unit that gets repeated across a sheet of paper. Download Tess, a computer program that aids in the design of such tilings; and browse a gallery of works created with the application.
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