 Cipher Challenge  University of Southampton
A cipher challenge for cryptographers under the age of 19. With solutions and comments about the breaking of sets of encoded messages, or ciphertexts, of increasing difficulties.
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 Circle Drawing Experiment  Thomas Denney
Draw a figure on the grid by clicking and dragging. Upon release of the mouse button, this JavaScript calculates a "perfect circle" accuracy score by using the sketch's perimeter as the circumference of a perfect circle, and comparing its area to the
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 Circle Formulas (Ask Dr. Math FAQ)  Math Forum
Formulas for finding the area, perimeter, arc, segment, or sector of a circle.
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 Circle Formulas  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about circle formulas, including how to find their circumferences and areas.
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 Circle Graph  What Percent?  NASA Lewis Learning Technologies Project
This circle graph shows how Jimmy spent his time during the last 24 hours. What percent of time did he spend watching television? A detailed answer is provided. From NASA's 9th Grade Math Proficiency Test.
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 Circles  360 Degrees  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about why a circle has 360 degrees, and the origin of that degree measurement.
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 Circles and Spheres (The Geometry Junkyard)  David Eppstein, Theory Group, ICS, UC Irvine
An extensive annotated list of links to material on circles and spheres.
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 Circle Scribe Disk Compass  Bill Harper
A new instrument for manually exploring shape and space, used to draw diagrams on paper, from cartoon characters to limacons, as well as standard geometric constructions. Unlike toys like spirograph, the Circle Scribe Disk Compass requires some geometrical
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 Circles  Diameter, Circumference, Radius and the Discovery of Pi (SMILE)  Kathleen Ryan, Randolph Magnet School
A 7th grade lesson designed to help students identify and measure the diameter, circumference, and radius of a circle. The students discover the approximate value of pi through the relation between the diameter and circumference. From the Geometry and
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 Circles in Geometry  Lesson Ideas: Math: Geometry; Teachnet.Com
Wholeclass and group activities for teaching circle concepts, pi, circumference, etc.
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 Circles in the Sky  Ivars Peterson; Science News Online
Detecting the shape of the universe: evidence of a finite, multiply connected universe may show up in microwave data from future spacecraft.
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 Circles of Dissonance  Ivars Peterson (MathTrek)
Much of today's music rests upon ancient tradition going back thousands of years to the time of the Greek mathematician and mystic Pythagoras. The Pythagoreans observed that tones an octave apart are pleasing to the ear. In modern terms,
one can say
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 Circles of Light: The Mathematics of Rainbows  Frederick J. Wicklin, Paul Edelman; The Geometry Center
How are rainbows formed? Why do they only occur when the sun is behind the observer? If the sun is low on the horizon, at what angle in the sky should we expect to see a rainbow? This lab helps to answer these and other questions by examining a mathematical
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 Circles of Light: The Mathematics of Rainbows  Steven Janke; The Geometry Center
How are rainbows formed? Why do they only occur when the sun is behind the observer? If the sun is low on the horizon, at what angle in the sky should we expect to see a rainbow? This lab helps to answer these and other questions by examining a mathematical
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 Circle Zap  Michael Bulmer
A Java applet that gathers data on your ability to use a mouse rapidly and accurately, with suggested questions for classroom activities.
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 Circular Reasoning  TJ Leone, Leone Learning Systems, Inc.
A free, Javabased software tool for thinking about circles, sectors, segments, and angles. Based on Montessori principles of learning through the manipulation of objects. Activity cards included. For Windows computers only. Includes ideas and stories
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 Circumference of an Ellipse (Ask Dr. Math FAQ)  Math Forum
A discussion of the derivation of the formula for the circumference of an ellipse. Also discussions of the evaluation of the formula, and approximating the circumference.
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 Circumferences, Diameters, and Radii (SMILE)  Dwayne Belle, Fuller School
A lesson designed to teach students to measure circumferences in inches, and compute radii and diameters, given different circumferences. From the Geometry and Measurement section of a collection of almost 200 single concept lessons by the Science and
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 Citizen Maths  Ufi Charitable Trust
Free courses of selfpaced video tutorials, discussions, and handson activities to try out. Developed by Calderdale College (UK), with CogBooks, the Institute of Education, and Oxford Cambridge RSA (OCR).
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 The Civilization of the Mayans  ThinkQuest 1997
Essentially a school paper in web format, covering, briefly, Mayan art, astronomy, ballgame, books and hieroglyphics, class system, and number system, with rated related Mayan links and references, and an abouttheauthors section.
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 CK12
Providers of free, standardsaligned, open content in the STEM subjects. See, in particular, the CK12 Foundation's flexbooks: customizable, free, curriculumaligned K12 math textbooks. In addition to dozens of student editions, some math flexbooks feature
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 ClarisWorks Graphing: Spreadsheet Lessons  Suzanne Alejandre
Stepbystep directions for using ClarisWorks spreadsheets, helpful in exploring the differences between exponential functions and linear functions. Bar graphs, pie charts, pictograms, and other graphs for linear, polynomial, and exponential functions.
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 Clash of the Chess Titans  Keith Devlin (Devlin's Angle)
Thoughts on the KasparovDeep Blue match of 3 May 1997. Throughout history, people have been building machines that can perform tasks better than humans. When Kasparov, referring to his upcoming match, talks about "an area that defines human beings,"
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 Class2Class  Melanie Sprouse
Class2Class is a clearinghouse designed to facilitate student and class participation in Internet projects, including collaborative projects, datacollecting experiments, peer tutoring, and keypal exchanges designed to enhance the mathematics in your
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 Class Champ multiplication & division
Software intended to help children learn the times table by heart using Pop Times Table songs; show how multiplication works by displaying the question graphically; and quicken the child's ability to recall answers and allow the child to practice questions.
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 class.com  Class.com, Inc
Class.com provides distance education over the Internet, and offers a complete high school diploma from a fully accredited, universitybased independent study high school. Math course listings include a math skill review, basic mathematics, beginning
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 Classes With Web Resources  University of Illinois at UrbanaChampaign (UIUC)
A list of University of Illinois hypertext courses that are using the Web to augment traditional instructional materials, covering, among other topics, Civil Engineering, Computer Science, and Mathematics. Follow the links to read the course descriptions
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 Classical and Quantum Chaos, A Cyclist Treatise  Predrag Cvitanovic'
An online textbook on chaotic systems and dynamics, including exercises, solutions, and a guide to related literature. Read the book online in hyperlinked PDF format, or download it as a gzipped PostScript file. By the CATS cyclist team: Cvitanovic',
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 Classical Dynamics: Spinning Eggs — A Paradox Resolved  H. K. Moffatt and Y. Shimomura, Nature
"If a hardboiled egg is spun sufficiently rapidly on a table with its axis of symmetry horizontal, this axis will rise from the horizontal to the vertical. Conversely, if an oblate spheroid is spun sufficiently rapidly with its axis of symmetry vertical,
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 The Classical & Keynesian ADAS Model of the Canadian Economy  Elmer G. Wiens; Egwald Web Services Ltd.
Macroeconomics model of the Canadian economy considering both the aggregate supply and aggregate demand for products. Illustrated article with interactive supplemental page.
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 The Classical Simplex Method  Prof. Hossein Arsham; University of Baltimore
A companion site to Arsham's Applied Management Science course. This introduces the simplex method for solving linear programming problems by first discussing the algebraic solution and pivoting row operations.
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 Classic Fallacies  Philip Spencer; University of Toronto Mathematics Network
Mathematical "proofs" demonstrating, among other things, that 1 = 2 and that all people in Canada are the same age. Each consists of several steps, and users search for the flaws. For every step there is explanation of why the flaw is or is not in that
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 Classic Iterated Function Systems  Larry Riddle
These pages investigate several of the classic iterated functions systems
and their associated fractals. Each IFS consists of affine transformations
involving rotations, scalings by a constant ratio, and translations. For
each example is given
* a
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 Classic Problems  Math Forum; Ask Dr. Math FAQ
Classic problems from the Ask Dr. Math FAQ (Frequently Asked Questions) files, including: age word problems, birthday probability, boy or girl?, camel and bananas, coin problems, doubling pennies, grazing animals, liars and truthtellers, the missing dollar,
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 Classification of Patterns  BrownHerbst, Donnelly, Stratton, AndersonNielsen; The Geometry Center
Materials about symmetry and classification of repeating patterns for students in grades 710 using wallpaper patterns, to be used as either an introduction or a review: a classroomready source of information. A final project created for Math 5337, Technology
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 Classification (SMILE)  Delores B. Wilburn, Shakespeare School
A lesson designed to motivate students to understand classification, and to teach decisionmaking, how certain objects relate to the number system, and the meanings of some words used to express mathematical ideas. From the Patterns and Logic section
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 Classifying Numbers  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about classifying numbers, such as "How are the different types of numbers related?" and "What is a real number?"
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 ClassK12.com  LogTera
Online adaptive math apps designed for distributed practice. Aligned to the Common Core State Standards (CCSS), ClassK12's K5 gamebased interactive environment and visual models reward students with points and badges. Freely access worksheets and practice
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 Classroom Books and Libraries: Math  Attanasio & Associates, Inc.
The mathematics selection from this vendor of classroom libraries and books, which include Big Al and Shrimpy, It's about Time, My Very First Book of Shapes, The Shapes We Eat, How High Can a Dinosaur Count?, Everyone Uses Math, Pigs on a Blanket, Underwater
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 Classroom Capsules and Notes  MAA Online
Classroom Capsules and Notes brings together the best of 114 years of the short classroom materials from the MAA print publications. These materials are free to everyone.
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 Classroom Compass  Adams, Powell, Assoc. Editors; Southwest Educational Development Laboratory
A magazine published from 1994 to 2005, with ideas, activities, and resources for teachers interested in improving instruction in science and mathematics, and links to simple classroom activities with ideas about learning and instruction. Each issue presents
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 Classroom Conversation (Learning and Mathematics)  Nicholls, Hazzard; Math Forum
In their 1993 book Education as Adventure, John Nicholls and Susan Hazzard explore students' understandings of the nature and point of school learning and the idea that students are valuable critics of the classroom curriculum and their own learning.
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 Classroom Projects  TEAMS Distance Learning, Los Angeles County Office of Education (LACOE)
A site for teachers looking for a content area project or contest for the classroom. Join a TEAMS project or browse a list of projects and contests sponsored by other organizations. Extensive list of upcoming, current, ongoing, and completed projects
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 ClassteacherCTLS
Short instructional math videos from the YouTube channel of Classteacher Learning Systems, the makers of iPerform and other interactive classroom technology: Counting Numbers, Decimal Fractions, and more.
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 ClassZone  McDougal Littell, Publishers
In ClassZone, McDougal Littell has gathered together all of its activities, interactive online resources, research links, chapter quizzes, and other materials that support its popular middle and high school mathematics textbooks, such as Integrated Math
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 Clay Mathematics Institute  Clay Mathematics Institute
The primary objectives and purposes of Clay Mathematics Institute (CMI) are to increase and disseminate mathematical knowledge, to educate mathematicians and other scientists about new discoveries in the field of mathematics, to encourage gifted students
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 Cálculo Contractivo
In Spanish: Nuestro grupo de investigación se ha propuesto compartir conocimientos con aquellas personas que estén motivadas para el estudio de la matemática o que puedan interesarse en conocer métodos no convencionales en Cálculo Numérico ó en áreas
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 Clear Educational Solutions  Calvin Leung
Product and order information for InstaGraphs, PostIt Notes® printed with a grid for use as graph paper. Also includes a student survey and suggestions for using InstaGraphs as a fundraiser.
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 Cleave Books
Teacher Resources on Line (TRoL) include downloadable grid paper; Ttiles; dictionary exercises; shapes Bingo; MisMaths, an annotated collection of innumeracy and other math mistakes in news headlines; fact sheets; tables; formulas; a mathematical vocabulary
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 CLICAL  Pertti Lounesto; Helsinki Institute of Technology, Finland
A calculatorlike Windows/DOS computer program for vectors, complex numbers, quaternions, bivectors, spinors, and multivectors in Clifford algebras, intended for researchers and teachers of Clifford algebras and spinors. CLICAL works directly on intrinsic
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