 Rolling with Reuleaux  Ivars Peterson (MathLand)
Why is the cover of a manhole round? The usual answer is that a circular lid, unlike a square or hexagonal cover, won't fall through the opening. The circle works because it has a constant width, defined as the distance between a pair of parallel lines
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 Rolocu: the Colour Twist Puzzle  Charles Edge
Use logic and planning to put the pieces into place so that all rows and columns have all the colours in them.
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 A Romance With Numbers  K. Venkatasubramanian
Biographical information and thoughts about Srinivasa Ramanujan, from The Hindu, December 24, 1993.
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 Roman Numeral Date Conversion Guide  Christopher Handy
A guide to deciphering Roman numeral year dates as commonly found in both modern and early printed books, including a Java applet that accepts Roman numeral input in the range 14,999 and converts it to Arabic form. The page explains the basic principles
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 Roman Numerals 101  Oliver Lawrence
The Romans used only seven letters; the combination of a letter and its position could represent any number. They also used a line above the letter, so the numbering system actually represents our own very closely, with fourteen different symbols. The
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 Roman Numerals and Dates  Paul Lewis
An illustrated introduction to Roman numerals, including Roman dates and calendar conversion, history and uses, a page on The Great 1999 Question, and a quiz. Three conversion tables are provided: Numerical 11449; Numerical 14502100; and Alphabetical
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 Roman numerals and decimals (Classics log)  John Durham
A letter to a Classics mailing list about the origin of and ease of calculation with Roman numerals.
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 Roman Numerals  Math Forum, Ask Dr. Math FAQ
Basics: How do I read and write Roman numerals? What are the rules for subtracting letters? How do I write large numbers? Web resources: introductions, charts, calculators, and converters. Calculations: Did the Romans use fractions?
How can I use Roman
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 The Roman Press, Inc.  Steven Roman
Home page of a California mathematics professor, including research articles, books and textbooks, and software.
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 Ron Blond  Ron Blond
Circle geometry applets to explore inscribed and central angles, tangents and radii, and tangents and inscribed angles. Also, applets illustrating the quadratic function (completed square and the discriminant), transformations of the sine and cosine functions,
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 The Roots of the Equation  James Cleveland
Blog by a high school algebra teacher in New York City "trying to figure out how it all fits together ... [and] creating interdisciplinary problems, projects, and thinking." A Math for America (MfA) fellow, Cleveland has blogged since June, 2011, with
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 Rosebush Math Line Puzzles  Math Forum
Three puzzles: 1) plant 7 rosebushes so that they form 6 straight lines with 3 rosebushes in each line. 2) plant 10 rosebushes in 5 straight lines with 4 bushes in each line. 3) plant 19 rosebushes in 9 straight lines with 5 bushes in each line. Questions,
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 Rossman/Chance Applet Collection  Franciso Garcia, Carlos Lima, and Beth Chance
Applets for simulating confidence intervals for population parameter, tintervals for different population shapes, behavior of regression line, histogram bin width, sampling Reeses Pieces, sampling 2002 U.S. Senators, sampling pennies, sampling words
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 ROSSMANCHANCE.COM  Allan J. Rossman & Beth L. Chance
Workshops and presentations, publications, and current projects by the authors of the Workshop Mathematics Project textbooks. See tables of contents, instructor guides, sample syllabi and exams, and answers to activities from books in the Workshop Statistics
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 The Ross Program  The Ohio State University
For high schoolers, the OSU Department of Mathematics offers an intensive summer experience designed to encourage motivated precollege students to explore mathematics. Over the course of eight weeks, students are immersed in a world of mathematical discovery.
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 Rotations (SMILE)  Susan Nash, Lake View High School
A lesson designed to teach students to define rotation as the composite of two reflections over intersecting lines; identify rotation images of a figure; and recognize and apply the properties of rotation. From the Graphs and Visuals section of a collection
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 Rough math: Focusing on rogue waves at sea  Ivars Peterson  Science News Online
Ocean currents and large fields of random eddies can focus a steady ocean swell to create unusually large waves. A current or eddy field acts like an optical lens to focus the wave action, says applied mathematician Bengt Fornberg of the University of
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 Rounding a Decimal  NASA Lewis Learning Technologies Project
Round 12.5861 to the nearest hundredth. A detailed answer is provided. From NASA's 9th Grade Math Proficiency Test.
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 Rounding Numbers  Math Forum, Ask Dr. Math FAQ
How do you round a number to the nearest tenth (10th), hundredth (100th), thousandth (1000th), etc.?
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 Rounding Seconds  NASA Lewis Learning Technologies Project
Erv ran the 110 meter high hurdles in 13.27 seconds. His teammate, Willie, ran the same race in 12.91 seconds. Rounded to the nearest tenth of a second, how much faster was Willie's time? A detailed answer is provided. From NASA's 9th Grade Math Proficiency
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 Rouse Ball's Fallacy  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
A famous fallacy by Rouse Ball now implemented in Java. A proof that an obtuse angle is right. How can that be?
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 Route ICS (formerly DeweyWeb): Interactive Communications and Simulations  Univ. of Michigan
An effort to link distant schools and expand the classroom experience: using telecommunications and computer conferencing, students can spend part of every school day in a "global classroom." Crossroads: The Route 12 Project is a grassroots attempt to
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 Row Your Boat  Ivars Peterson (MathTrek)
Although a rowing shell with eight rowers is much larger than one with a single rower, all shells have roughly the same proportions (at least for the surface area over which the shell makes contact with water). Data from 2000meter world and Olympic championship
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 Roxanne Eckenrode's Storefront  Lulu.com  Free SelfPublishing  Roxanne Eckenrode
Selfpublished math worksheets. Several are free. They are downloadable and printable; correct answers will spell out a message or fill in a puzzle.
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 Royal Tyrrell Museum of Palaeontology
Virtual site for a science museum named for Joseph Tyrrell, who in 1884 travelled to what is now Alberta, Canada to study coal deposits and found the first dinosaur remains ("Albertosaurus") in the Drumheller area. The museum's mandate is to collect,
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 RSA Laboratories' Frequently Asked Questions About Today's Cryptography  RSA Laboratories
Cryptography FAQs organized into eight chapters: introduction, cryptography, techniques in cryptography, applications of cryptography, cryptography in the real world, laws concerning cryptography, miscellaneous topic, and further reading. With appendices
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 R. S. Schaeffer  Randy S. Schaeffer, Math & Computer Science, Kutztown University of Pennsylvania
Schaeffer teaches a course called "Methods of Teaching Secondary Mathematics." Download the lessons created by his students that call on Geometer's Sketchpad, graphing calculators, and Microsoft Excel. Lesson topics address parallel lines, box and whisker
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 Rubik's Cube Information  Michael Reid
All about Rubik's Cube  even a mailing list. Site contents include: the Nederlandse Kubus Club; Rubik's cube pages on the Web; Cube books; Sources of cubelike puzzles; the author's notes, including an optimal cube solver; other Cube solutions on the
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 Rubik's Cube Java Applet  Michael Schubart
To twist the cube, press the mouse button over a cubelet face that belongs to the slice you want to move. Keeping the button pressed, drag the mouse in the desired direction; then release the button. Moving the whole cube is done in the same way  just
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 Rubik's Games  Androsoft
Dedicated to the first PC CDROM game from Erno Rubik, Rubik's Games contains 5 subgames: Rubik's Classic, Cover Up, Paint War, Rubik's Playground and ZigThrough. Download the Rubik's Games Web Site Plugin plugin or a demo of the Rubik's Game CDROM.
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 Rubik's Online  Rubik/Seven Towns
The official online site for the Rubik's cube. Play with the cube and other Rubik's games and puzzles online; find information on where to buy Rubik's products; use the forum to exchange views, opinions, comments, suggestions and anecdotes related to
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 Rubix Corner  Duane Cash
The site includes information regarding the Duane Cash Cube Collection now featured at Hessport's Rubikshop in their "collectibles" section. New puzzles include the Rubik's Triamese, Fusion, Fusion+, SpeedFusion, 5x3, and 4x3 Cubes, which give those interested
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 Rudi Mathematici  Rudy d'Alembert, Alice Riddle, and Piotr R. Silverbrahms
Matematica, giochi matematici, problemi, indovinelli e farneticazioni. Soprattutto una rivista, RM contiene Il Compleanno, Problemi del Mese, Bungee Jumpers, Soluzioni e Note, Quick & Dirty, Pagina 46, Paraphernalia Mathematica, Allegati ed Eventuali,
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 Rungs and Vineyards  Paul Kunkel
Investigations of two interesting visual effects seen from a moving automobile. It includes two interactive perspective drawings, and a discussion of the
cylindrical and planar projections used to create them.
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 Runiter Company  Saeid Nourian
Demo or purchase software that plots math functions in 3D or in or grid sheets, rotates them, and manipulates them in realtime: Smart Math Calculator, Graphing Calculator, A&G Grapher (algebra and geometry), Statistics Problem Solver, and Calculus Problem
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 Russian Peasant Multiplication  Math Forum, Ask Dr. Math FAQ
What is Russian peasant multiplication? How do I use it? Why does it work? How is the Russian peasant algorithm connected to binary numbers?
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 Russian School of Mathematics
An afterschool math enrichment program "based on the best practices of advanced math schools in Russia and Europe and adapted to the US educational environment." Cofounded in 1997 by Inessa Rifkin and Irina Khavinson — who recall that, in the
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 Rymar  Rymar Applications
"Helping with math homework and concepts one app at a time." The Cramer's Rule app finds the solution of a system of equations with 2 or 3 unknown variables, and also reveals — via the "Help" button — all of the intermediate determinants.
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 Sabermetrics  The Baseball Archive
"The search for objective knowledge about baseball." Read a primer of Bill James' findings, or David Grabiner's manifesto on Sabermetrics. Studies address minor league equivalencies ("Are minor league stats a good precictor of major league performance?"),
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 Sabernomics: Economic Thinking about Baseball  JohnCharles Bradbury
A blog on the economics in, and of, the game of baseball. Original tools and studies includes salary estimators, research on age and hitting and pitching, antitrust and Major League Baseball, attendance and winning, Barry Bonds and walks, competition
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 SABER  The World Bank Group
An open data tool that provides comparative data on education policies around the world. The Systems Approach for Better Education Results (SABER) web tool aims to help countries collect and analyze information on their education policies, benchmark themselves
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 SABES: System for Adult Basic Education Support  Massachusetts Department of Elementary & Secondary Education
SABES promotes high quality adult basic education services through training, support, and resources that improve the skills and knowledge of practitioners and strengthen programs. SABES strives to achieve this mission by: providing staff development that
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 SACNAS Biography Project  Society for the Advancement of Chicanos and Native Americans in Science
Highlights of the life stories and professional contributions of Native American, Chicano and Latino scientists, mathematicians, and engineers. The Project was created so that K12 students could see themselves reflected in the stories of the lives that
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 Sacramento Area Math Help and Tutoring  Just Math Learning Centers
Just Math provides math help, tutoring and SAT prep for Sacramento area children through college students. Skills training in elementary math, algebra, geometry, and calculus.
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 Sacred Geometry  Bruce Rawles
"In nature, we find patterns, designs and structures from the most minuscule particles, to expressions of life discernible by human eyes, to the greater cosmos. These inevitably follow geometrical archetypes, which reveal to us the nature of each form
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 Sacred Geometry Discovery  J. Vincent Beall
The Platonic solids are used to organize theosophical terms. The five regular solids are the basis for a threedimensional map of the Kabbalistic Tree of Life.
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 Sage: Open Source Mathematics Software  William Stein, University of Washington
An open source mathematics program designed to do everything from map a 12dimensional object to calculate rainfall patterns under global warminganything Maple, Matlab, or Mathematica would do. This free software reveals how it performs its calculationsso
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 Salinon: From Archimedes' Book of Lemmas  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
A description of Archimedes' application of propositions from the second book of Euclid's Elements to mathematical proofs. An interactive Java exploration is provided.
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 Saltire Software
Mathematical technology for industry and education. Saltire Software's core technologies are constraintbased interactive geometry systems, symbolic algebra, and optimization, with products for mechanical engineering, mathematics education and layout
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 SAM Learning  SAM Learning Ltd.
U.K. exam revision (review) for A Levels (age 1618), GCSEs (age 1416) and SATs (KS3, age 1114; KS2, age 711; KS1, age 57). Draganddrop exercises and online tests of math knowledge.
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