 Countdown!  Objective Consulting Inc. (OCI)
Calculate the number of seconds between any two events: find out how long it will be until the millennium, until your birthday, or simply how long you have been alive. Answers are also expressed in days, hours, and minutes.
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 The Counterfeit Coin  Ivars Peterson (MathTrek)
The classic puzzle of the counterfeit coin has long served as a stiff test of one's reasoning power and ingenuity. In its standard form, the problem concerns 12 coins identical in size, shape, and appearance. One coin, however, is counterfeit, having
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 Counting by Twos  Ivars Peterson (MathTrek)
How much is a megabyte? Many people don't really know. The problem originated decades ago when computer professionals noticed that 2^10 is very nearly equal to 1,000, and they began using the metric prefix "kilo" to mean 1,024. That was okay when computers
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 Counting Hamilton Cycles in Product Graphs  Frans Faase
Exploration of Hamilton paths through a program which draws a snake that starts at one place in a box, and then extends itself until it cannot go further, after which it shrinks again, to seek another path. The author coded these snake programs in Fortran,
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 Counting: The Beginning of Mathematics  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
An introduction to and a detailed description of the process of counting, with applets for exploring addition, multiplication, and division.
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 Counting to Calculus: Mathematics  William K. Bradford Publishing Co.
Math software, printed supplements, workbooks, textbooks, posters, and teacher tools available for Elementary, Middle and Secondary math curriculum.
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 Counting Triangles  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
Division of a square by evenly spaced lines parallel to its sides yields a number of small squares which is clearly square. Interestingly, the same is true for a triangle divided by evenly spaced lines parallel to its sides. The page contains a dynamic
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 Count Mathula  Michelle Anderson
Worksheets for Anderson's Algebra III and Trigonometry classes, available as MS Word downloads, editable using MathType, and also as PDFs: functions, complex numbers, trigonometry. Resources include premade graph paper in PDF format to download.
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 Count On  Department for Education and Employment, UK
Activities and resources  some simple and some fancy  for parents, teachers, and students. Resources offers, among other things, guides: to mathematical misconceptions; for parents helping with homework; for promoters of math fairs; and for providers
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 A Course in Number Theory for High School Students  David Garlock
For students who have completed algebra, geometry, trigonometry, precalculus
and calculus and are looking for new challenges. It could also be taken as a summer course or as an independent study in the midst of the traditional math sequence. Download
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 Course Project Suggestions (Geometry and the Imagination)  Conway, Doyle, Gilman, Thurston; The Geometry Center
An list of suggestions for projects in geometry, topology, symmetry, making geometric solids, calendars, spherical and hyperbolic trigonometry, puzzles, models, etc. Projects were to be exhibited at the Geometry Fair at the end of the course.
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 CourseServer  Jud Cornish; Fairbanks Country Day School, San Diego, CA
A Webhosted math problem generator that allows you to select from thousands of different problem types and automatically generate problemandanswer worksheets in your browser that can be printed out. Choose from a list of courses from Grade 1 (beginning
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 Covering and Packing (The Geometry Junkyard)  David Eppstein, Theory Group, ICS, UC Irvine
An extensive annotated list of links to material on covering and packing problems.
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 Covering Up (MatheMUSEments!)  Ivars Peterson (Math Muse for Kids)
Have you ever wondered why the cover of a manhole is nearly always round? Why couldn't it be oval or square? The usual answer is that a circular lid, unlike a square or an oval cover, won't fall through the opening, but the circle isn't the only shape
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 The Cow in the Classroom  Ivars Peterson (MathLand)
Math Curse by Jon Scieszka and Lane Smith spoofs the types of word problems that educators and textbook writers invent to dress up arithmetic exercises and, supposedly, to demonstrate the relevance of math to everyday life. Canadian economist and humorist
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 CPMPTools  CorePlus Mathematics Project (CPMP)
CPMPTools is a suite of both general purpose and custom software tools designed to support student investigation and problem solving in the 2nd edition CorePlus Mathematics texts. The CorePlus Mathematics Program was one of five designated as "exemplary"
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 CPO Online  Cambridge Physics Outlet
A company founded by teachers and scientists that creates handson equipment and curriculum for teaching science, math, and technology from grades 412 and beyond, and provides effective professional development in science and math that is both content
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 C Program Math Functions  Dave Norman
Examples of C coding for some maths problems. Current functions are atan
(double x), cos (double x), and sin (double x).
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 Cracking a Medieval Code  Ivars Peterson (MathTrek)
The first printed book on cryptology was written by Johannes Trithemius (14621516), an abbot in Spanheim, Germany, who was one of the leading intellectuals of his day. Bearing the title Polygraphiae libri sex ("Six Books of Polygraphy"), it was published
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 Cracking Kepler's spherepacking problem  Ivars Peterson; Science News Online
The familiar piles of neatly stacked oranges at a supermarket represent a practical solution to the problem of packing spheres as tightly as possible. Now, a mathematician has proved that no other arrangement of identical spheres fills space more efficiently.
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 Cracking the Myth of Ball Control  Ivars Peterson (MathLand)
Ball control has become common practice in a number of sports. In basketball, for example, coaches often urge their teams to slow down a game at certain times or to control its tempo. In professional football, "time of possession" has become a statistic
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 Crackpot Index  John Baez
A fun site which outlines how you can tell if a new theory is really from a "crackpot."
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 Crafty Puzzles  James Cole, The Crafty Puzzles Company
A U.K. establishment selling wooden puzzles of all sorts: jigsaw puzzles, puzzle boxes, brain teasers, models, and functional pieces.
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 A Crash Course in Symbolic Logic  D.J. Brasier; Math Forum, Ask Dr. Math FAQ
Is symbolic logic so hard that some people will just never be able to get it? In a gentle introduction to the notation and rules of derivation used in symbolic logic, Dr. Achilles shows why the answer to that question is 'No'.
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 Crashing Waves, Awesome Explosions, Turbulent Smoke and Beyond: Applied Mathematics and Scientific Computing in the Visual Effects Industry [PDF document]  Aleka McAdams, Stanley Osher, and Joseph Teran
The May 2010 issue of the Notices of the American Mathematical Society includes a PDF article (1.3M) entitled "Crashing Waves, Awesome Explosions, Turbulent Smoke, and Beyond: Applied Mathematics and Scientific Computing in the Visual Effects Industry."
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 CRC Press LLC
A scientific and technical publisher of books, journals, regulatory newsletters, and environmental seminars. A searchable online catalog may also be browsed by topic, among others Engineering, Computer Science, and Math & Statistics.
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 Create 2D and 3D gnuplot Graphs
Input a function, vary parameters, plot 2D, 3D Surface, or 3D Contour, vary range displayed, and plot multiple functions at once. With help on various features, and links to graphing animated plots and varying the parameters. Part of the Shodor Educational
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 Create a Graph  National Center for Education Statistics (NCES)
Create your own graphs online: bar graphs, line graphs, area graphs, pie charts, or XY graphs (line, bubble, or scatter plots from Cartesian coordinates). Enter your own data, choose your own labels, preview your work, then print or save your graphs.
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 Creating NCubes  Dennis Clark
Web and PowerPoint files for learning how to make tesseracts, draw nspace cubes, and chase snakes, or certain closed paths (loops), in nspace cubes. Also, download Ncubes.exe, a Visual Basic program to draw Ncubes.
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 Creative Geometry  Cathleen V. Sanders
Teachers and students will find creative and interesting "handson" projects for most topics in the geometry curriculum. Each project is designed to help students understand, remember, and find value in the concepts of geometry. The pages are organized
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 Creative Java Puzzles  J. L. Read, Enchanted Mind
Games "good for exercising both sides of the brain." Knight's Tour: pass all the squares of the board with the knight, making only legal moves. Peg Solitaire: Remove all the pegs in the least amount of time, finishing with only one peg in the target hole.
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 Creative Problem Solving  Rob Eastaway
Eastaway's "portfolio" of interests includes short descriptions of his school talks, newspaper articles, and books he has authored or coauthored, such as Maths for Mums and Dads, The Hidden Mathematics of Sport, How to Remember Almost Everything, Ever,
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 Crewton Ramone's Blog of Math  Crewton Ramone
Ramone's blog, which dates back to July, 2009, has included posts  many with video  such as "Fractions Despite SPED," "Why Invert and Multiply," "4 Year Old Math Enrichment," "Fractions and Addends," "Fractions and Autism Do in Fact Mix," and "Fraction
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 Critical Evaluation Information  Kathy Schrock's Guide for Educators, Discovery School
With the advent of the World Wide Web and the huge amount of information it contains, students need to be able to evaluate a Web page for authenticity, applicability, authorship, bias, and usability. To help teachers get students started with this process,
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 Critical Issues in Mathematics (NCREL)  Pathways to School Improvement
Articles from the North Central Regional Educational Laboratory (NCREL). The Significance of the NCTM Standards; Ensuring Equity and Excellence in Mathematics; Locating, Using, and Integrating InternetBased Mathematics Materials; Providing HandsOn,
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 Critical Thinking Books and Software
Critical thinking books and software for home and classroom for use in mathematics, science, language arts, social studies, and more. Search for Content Area Mathematics from the classroom catalog or the home catalog.
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 Critical Thinking Puzzles  Eldhose
Puzzles, logical thinking riddles, word problems in blog format. Comment with your solution and read others' workings.
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 Critic of Technology in Schools Faces Tough Audience  Pamela Mendels
From the New York Times column on Education, an April 1998 report on public opinion of the views of Todd Oppenheimer (author of "The Computer Delusion", which apperared in the Atlantic Monthly magazine), from a public meeting concerning technology in
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 CROC'Sciences: le net.magazine de la pédagogie des sciences  P. Lambert
Un mensuel faisant le tour des sites scientifiques d'intérêt
pédagogique, soit pour la construction d'un cours, soit pour les
élèves euxmêmes. Chaque numéro comporte 6
catégories: Mathématiques,
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 Crop circles: Theorems in wheat fields  Ivars Peterson  Science News Online
Patterns of circles and triangles surreptitiously flattened into the crops of southern England reveal the perpetrators' sophisticated knowledge of Euclidean geometry.
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 CrossAge Tutoring  Marah Fortson; Math Forum
An annotated bibliography: articles to help teachers deal with a classroom of learners with different abilities, different strengths and weaknesses, who are at different levels academically, behaviorally, and socially. The task of the teacher is a challenge,
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 Cross Number Puzzles  Rainer Typke
Cross number puzzles to solve online; log in to create your own. Also known as crossfigure, figure logic, or numberlock puzzles, cross number puzzles require numbers instead of words to complete a crosswordlike grid.
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 Crossroads in Mathematics: Standards for Introductory College Mathematics Before Calculus  American Mathematical Association of TwoYear Colleges (AMATYC)
A searchable book on the Web that addresses the need to establish standards for the mathematics programs that bridge the gap between high school mathematics and college calculus. It also aims to satisfy the needs of students who do not plan to study calculus.
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 CRUX Mathematicorum with Mathematical Mayhem  Canadian Mathematical Society
The Digital Supplement to the Canadian Mathematical Society's Problem Solving Journal, for those who practice or teach mathematics. Published eight times per year, the materials at this site are available to all subscribers of CRUX; a sample issue is
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 Cryptarithmetic Puzzle Solver  Naoyuki Tamura
Enter a cryptarithm or select an example, such as SEND + MORE = MONEY. Also, puzzle generators based on themes such as color names, fruits, vegetables, and numeral words in English, French, German, Spanish, and Italian.
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 Cryptarithms  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
Cryptarithms are brain teasers obtained when digits in numerical calculations have been replaced by letters. Customarily, distinct letters stand for different digits. Another term, Alphametics, denotes cryptarithms in which letters form meaningful words,
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 Cryptarithms Online  Jorge Soares
Mathematical puzzles in which the digits are replaced by letters of the alphabet or other symbols. Brainteasers by the author; cryptarithms from the journal Sphinx; a primer; books on cryptarithms, and links to relevant sites on the Web.
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 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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 Cryptography AZ  SSH Communications Security
An introduction to the basics of cryptography: Basic Terminology; Basic Cryptographic Algorithms; Digital Signatures; Cryptographic Hash Functions; Cryptographic Random Number Generators; Strength of Cryptographic Algorithms; Cryptanalysis and Attacks
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