 The Crypto Drop Box of the American Cryptogram Association  Jerry Metzger
The American Cryptogram Association (ACA) is a nonprofit volunteer organization devoted to disseminating cryptographic knowledge. Members make up and solve their own creations strictly for the fun of it. Every two months, the ACA journal, The Cryptogram,
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 A Cryptographic Compendium  John Savard
A book about cryptography with information about a large number of cipher systems and a limited coverage of cryptanalysis. It is mostly concerned with the various kinds of ciphers people have used and only mentions a few things about breaking ciphers.
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 Crystals: Crystallography & Systems  Suzanne Alejandre
A Math Forum Web Unit. Students studying polyhedra enjoy seeing the structures as they occur in the real world. Crystalline structures can be categorized into seven crystal systems: see photographs of beautiful crystals or make paper models of crystals
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 CS Bits & Bytes  The National Science Foundation
CS Bits & Bytes highlights innovative computer science research, often at the intersection with other disciplines, and includes profiles of the individuals in the field, links for further exploration, and interactive activities. Past issues of the
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 CSMC: Center for the Study of Mathematics Curriculum
An NSFfunded project serving the K12 educational community by focusing scholarly inquiry and professional development around issues of mathematics curriculum. Major areas of work include understanding the influence and potential of mathematics curriculum
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 CTAP Middle School Math Project  CTAP Region IV
A database of online technology resources supporting California middle school math content standards for grades 6, 7, and algebra. Designed for use in classroom instruction or as homework helpers for students, the matrices resources align to state standards
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 The CTK Exchange  Interactive Math Miscellany and Puzzles, Alexander Bogomolny
A page devoted to questions and answers concerning Bogomolny's pages and math in general. Postings are approved by Bogomolny, and usually answered by him, although they may be answered by the general public as well. Posting topics vary all the way from
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 CTK Math Games for Kids  Interactive Math Miscellany and Puzzles, Alexander Bogomolny
This site presents a collection of Javabased interactive games and puzzles with mathematical contents and a few practice exercises disguised as games. Alexander Bogomolny, the site's author, writes, "There are a few games whose purpose is to allow for
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 CubeIt  Education Development Center, Inc. (EDC)
A math group activity: you will need fifty cubes per group. Gather sugar cubes, wooden cubes, units from Dienes blocks or Cusinaire rods, or any manipulative that has a cubical shape. Students will: estimate the dimensions of the largest cube that can
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 Cube Roll  Cary and Michael Huang
Use the arrow keys to steer a cube along a path of squares towards a final square. Each successive level poses new restrictions based on which faces of the block can or cannot roll onto the square path, making a game out spatial thinking of polyhedral
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 Cubes of Perfection  Ivars Peterson (MathTrek)
...Six is the smallest perfect number. Twentyeight comes next. Its proper divisors are 1, 2, 4, 7, and 14, and the sum of those divisors is 28. Incidentally, if the sum works out to be less than the number itself, the number is said to be defective
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 Cubeworld  Hank Gross
Cubeworld: an adventure in solid geometry. This book, with 21 illustrations by the author, is in the tradition of Edwin Abbott's classic Flatland and explores what might happen if the Earth were transformed into a cube. Gravity is different, rain falls
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 CUE (ComputerUsing Educators)  CUE, Inc.
A nonprofit California educational corporation that supports an active membership of more than 10,000 professionals from within and outside California, in schools, community colleges, colleges, universities, related institutions, and related fields.
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 CueThink
Makers of social, collaborative, interactive learning environments such as CueThink, a peertopeer iPad application for grades K12.
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 Cuisenaire Math  ETA/Cuisenaire
From the makers of Cuisenaire Rods: Connecting Cuisenaire Rods, Cuisenaire Roddles (board games and puzzles that emphasize spatial reasoning skills), Cuisenaire Rods for the Overhead, Magnetic Cuisenaire Rods, and other manipulatives. Publications include
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 Culturally Situated Design Tools: Teaching Math through Culture  Ron Eglash
Java for creating your own Mangbetu design, cornrow curves, graffiti, bead looms, SimShoBan, Yupik star navigator, Yupik parka patterns, PreColumbian pyramids, and rhythm wheels  and learning the mathematics behind them. Organized into African, African
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 CUNY Games Network  CUNY Academic Commons
Blog about the pedagogical uses of both digital and nondigital math games, how they improve student success, and how they encourage research and scholarship in the developing field of gamesbased learning. Posts, which date back to July, 2011, have included
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 Curious and Useful Math  Clay Ford
Tricks and rules for quickly calculating certain types of math problems, many from the 1888 book The Carpenter's and Joiner's Pocket Companion. Multiplication Tricks; Division Tricks; Squaring Tricks; Can it Divide...?; Age Math; Bible Numbers; Box Tricks;
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 Curmudgeon
Blog by a veteran math teacher in Vermont who "believes that math should be taught, not collaboratively explored; algebra and geometry are better than a vague course of Integrated Math; spiraling doesn't work nearly as well as learning it properly the
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 Curricula, Lessons, and Activities  ARTSEDGE
Annotated links on the Internet and additional offline resources highlighting lessons that interrelate the study of math with the arts. Organized into online curriculum, and related online resources of primary resources and indices.
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 Curriculum Development: NSF Awards  Mathematics Education at the Math Forum
A list of math curriculum development projects constructed by means of a text search of the NSF awards database. Each link leads to an abstract of the project, stored at the NSF World Wide Web Server. The first two digits of the numbers that appear to
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 Curriculum Development Projects  Mathematics Education at the Math Forum
The Math Forum's suggested sites on curriculum development in math education, including projects sponsored by the NSF and others.
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 Curriculum Guides: Math & Science  Star Tribune, Minneapolis/St. Paul, MN
The newspaper provides students with opportunities to apply their math skills to reallife problems and to read uptodate scientific information. Math You Can Bank on: reallife money and consumer skills; Mathematics in the News: from the simple calculation
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 Curriculum Issues  Beauregard Parish (Louisiana) Public Library
Links to sites with information about the new New Math, whole math, whole language, and traditional curriculum resources
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 Curry K. Software  Curry Kenworthy
Shareware for Education and Productivity: Pillbug Golf (Mac  learn about points, slopes, and angles while you putt); Snakey Math (Mac  the basic operations, arcade style); Galactic Geometry 3D (Windows  calculate volume and surface area of 3D objects
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 Curry's Paradox  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
A bewildering dissection paradox wherein recombination of 4 pieces cut of a rectangle produces a rectangle of a different size. Borders geometry and algebra. Accompanied by a Java illustration.
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 Curvature of Surfaces (Geometry and the Imagination)  Conway, Doyle, Gilman, Thurston; The Geometry Center
If you take a flat piece of paper and bend it gently, it bends in only one direction at a time. At any point on the paper, you can find at least one direction through which there is a straight line on the surface. You can bend it into a cylinder, or into
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 Curves on Baseballs  Ivars Peterson (MathTrek)
It's that time of year again (at least in North America), when the thoughts of many sports fans turn to baseball. Over the years, the game has also attracted the attention of mathematicians and statisticians intrigued by the rules, geometric considerations,
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 Cutting Corners  Ivars Peterson (MathLand)
Go to just about any college campus or public park and you're bound to see two kinds of trails: "official" paths defined by paved or gravel surfaces and "unofficial" routes trodden into the grass or dirt marking where pedestrians have preferred to walk
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 CYBERCHASE Online  Educational Broadcasting Corporation (PBS.org)
Companion site to CYBERCHASE, PBS's animated math adventure series, intended to foster math literacy and problemsolving skills for kids ages 811. Play interactive games or practice with tools such as the talking calculator, crack challenging puzzles,
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 Cyberkidz  Chato BV, touchscreensoftware.nl
A free website with more than 50 games about math, literacy and geography. In English and Dutch.
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 Cyberkidz.net  Chato BV
Online educational games for primary schools, widely used in the Netherlands and recently translated into English.
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 Cyberpapy  Boulanger
Posez votres questions des devoirs dans les forums; des "cyberpapys" répondent.
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 Cyberspace and the Classroom  SageNet
A June 1998 article collecting individual teacher and parent views of the effects of technology in the classroom, the best ways to use technology, and some favorite sites to visit in pursuit of education.
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 Cylinder Formulas (Ask Dr. Math FAQ)  Math Forum
Formulas for finding the surface area and volume of a general cylinder and a right circular cylinder.
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 Daeron's Java  Daeron Meyer
Numerous applets, created by a former technician at the Geometry Center, can be enjoyed here if you have a Java enabled browser. Mathrelated creations include a 3D viewer; Real time function graph; Rotating Red Triangle; Circle Text; and links to other
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 Daily Desmos  Anderson, Dan; Fenton, Michael; and Lanier, Justin
A daily challenge to reproduce a given graph using Desmos or some other graphing calculator. Teachers Anderson (NY), Fenton (CA), and Lanier (NY) rate the plots by difficulty. Also available from http://dailydesmos.blogspot.co.uk/.
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 Daily Dose of Teaching Awesome  John Mahlstedt
Blog by a math teacher in the Bay Area who also coaches track and basketball at his middle school. Posts on his "journey to find and document at least ONE good thing everyday of the school year" date back to January, 2014: "Desmos Brings the Noise," "Central
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 The Dalton School  New York, NY
Founded in 1919, the Dalton School is committed to educating students in accordance with the Dalton Plan developed by Helen Parkhurst in the progressive spirit inspired by John Dewey during the early 20th century. Curriculum includes: First Program, Middle
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 Dancing Chaos  Ivars Peterson (MathTrek)
Music, dance, and chaos... The image on the computer screen resembles a delicate, stylized butterfly with translucent wings held lazily askew. It's called the Lorenz attractor, named for meteorologist Edward N. Lorenz of MIT, who in 1963 discovered this
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 danicamckellar.com  Danica McKellar
From the author of the books for middle school girls, Math Doesn't Suck: How to Survive Middle School Math without Losing Your Mind or Breaking a Nail, Kiss My Math: Showing PreAlgebra Who's Boss, and Girls Get Curves. Read about McKellar's voiceover
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 Daniel Willingham
From the author of Why Don't Students Like School? and When Can You Trust the Experts? (subtitled: "How to tell good science from bad in education"). See, in particular, Willingham's articles, such as "Why transfer is hard," "Why students remember or
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 DapJ Music
Rap music for adolescents struggling to learn and retain math concepts: "Fractions Are Division Problems"; "Keep, Change, Change"; "Properties"; "First, Outer, Inner Last"; and more. The educationally based music production company provides Common Core
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 DareWare: Educational, Multimedia and Java Games
Educational games and multimedia products (free demo versions downloadable), Java games, "This Week in U.S. History", and a brief list of other shareware sites.
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 The Data and Story Library (DASL)
"Dazzle," an online searchable library of datafiles and stories that illustrate the use of basic statistics methods, providing data from a wide variety of topics so that statistics teachers can find realworld examples that will be interesting to their
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 Database of Number Correlations  James Barton
Partitionings, prime factorizations, polygonal numbers, and other data about each of the numbers one through one thousand, as well as connections to "various material and occult phenomena." See also Barton's magic square that has interesting prime factor
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 Data Games  KCP Technologies
As students play Data Games, they generate data that they must analyze to win the games. Supporting materials include a student worksheet; teacher guidelines that correlate the activity to the Common Core State Standards for Mathematics (CCSSM); and videos
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 The Data Library  Pat Daley
Ongoing datasharing projects, downloadable Excel spreadsheets, and other sources of data on the Web. Collaborative Projects  specific data collection projects that teachers and their students may become a part of; Data Sets that can be downloaded as
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 Datamath Calculator Museum  Joerg Woerner
Historical calculators and educational toys, primarily from Texas Instruments. History of calculators, technical details, many interesting sidelights, including downloadable emulators.
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 Data Paint  Man Machine Interface, Inc.
Statistical utility software for for MS windows 95, 98, NT4.0, 2000, that uses GUI (Graphical User Interface) language to link charts, graphs and statistical information about selected groups of data. For each graph and statistics window, there is a corresponding
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