 Digital Library  The Exploratorium, San Francisco
The Exploratorium AtoZ. Archived webcasts, web cams, past exhibitions: stills, movies, sounds, and other experimental items. Online versions of a few of the Exploratorium's interactive exhibits; the Exhibit CrossReference  an experimental database
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 Digital Mathematical Performance  Gadanidis, George; Borba, Marcelo; Hughes, Janette; et al.
Watch video, liveacted dramatic storyboards, and animations of how people "perform" mathematics: Flatland, "Help Me, Fermi," Should Parallel Lines Never Meet," "The Pleasure of Making 10" (linear equations), "The Waiter" (the missing dollar problem),
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 Digital Math  Santa Barbara County Education Office
A site to assist Algebra I, Grade 7, and Grade 6 students, their parents, and educators with the California State Mathematics Content Standards. Log in for Quicktime that provides stepbystep instruction to solve problems aligned with the mathematics
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 The Digit Connection  Lizzie
A tribute to the number pi through music, poetry, and fiction. (Meet Sailor Pi!) Also includes a brief history of pi with some ways to calculate it, a quote collection, and ways to celebrate the number  even if it's not Pi Day.
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 Digits, Squares, and Cycles  Ivars Peterson (MathTrek)
Fascinating patterns lurk among the digits of whole numbers. Pick a positive integer, such as 57. Square each of the digits, then add the squares together: 5^2 + 7^2 = 25 + 49 = 74. Do the same thing with the digits of 74: 7^2 + 4^2 = 49 + 16 = 65. Keep
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 DIMACS  Rutgers & Princeton Universities, AT&T Bell Labs, BellCore
The Center for Discrete Mathematics and Theoretical Computer Science, an NSF Science and Technology Center. DIMACS is devoted to the development of the interrelated fields of discrete mathematics and theoretical computer science, among the most rapidly
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 DimensionU
Creators of educational software that put the action adventure fun of mainstream video games in a learning environment that prepares students for high stakes exams. First person shooter games Dimenxian, Evolver, and Meltdown contain 3dimensional virtual
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 Dipping math scores heat up debate over math teaching...  Bridget Murray, American Psychological Association (APA) Monitor
... psychologists differ over the merits of teaching children 'whole math'. An APA newsletter article that outlines the debate over the effectiveness of whole math, a demonstrative approach where manipulatives help children understand math concepts. "Some
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 Disabilities and Math Anxiety  Math Forum, Teacher2Teacher FAQ
Answers to a frequently asked question: How can I help my child who has a physical or learning disability?
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 Discoveries & Breakthroughs Inside Mathematics  American Mathematical Society (AMS)
Read articles and watch video news segments about the latest discoveries and applications of mathematics: "Do the Math Dance," "Mathematician Calms the Skies with Turbulence Detection Algorithm," "Become a Smarter Shopper," "The Science Behind Movie Magic,"
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 Discover Magazine  The Walt Disney Company
The monthly magazine of science and technology. Covers space, biology, health, medicine, AIDS, computers, new technology, the environment, astronomy, ancient life, archeology, evolution, physics, mathematics, ecology, and more. Available online: selected
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 Discover TI Neighborhood Workshops  Texas Instruments, Inc.
The free Discover TI Neighborhood Workshop provides a handson beginner's introduction to TI graphing technology. There will be 25 workshops throughout the United States. There is a choice of six different topics that appeal to middle school and high
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 discretemath  Math Forum
A discussion group for subject matter concerning teaching and researching of discrete mathematics at all levels. It began as a closed list for the researchers and educators who participated in the Rutgers University Discrete Math and Theoretical Computer
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 Discrete Math Problem of the Week (PoW)  Math Forum
Discrete math problems from a variety of sources, including textbooks, math contests, NCTM books, and puzzle books, and reallife situations, designed to reflect different levels of difficulty. From 1999 until 2002, this service challenged students with
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 Discussing Undergraduate Mathematics Education on the Internet  Steve Weimar for MAA Online; The Math Forum
Descriptions of good math discussion groups: what kinds of conversations you will find, how to access them, etc. Teaching and learning mathematics: MATHEDU, AMTE, MATHEDCC, DEVELOPMENTAL MATH. Topicspecific lists: MATHHISTORYLIST, APCALC, APSTAT,
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 Discussion Groups: Technology  Texas Instruments
Read, search, and post to groups about TI products: Scientific Calculators, TI10, TI73, TI80/81, TI82/83/83 Plus/Silver Edition, TI85/86, TI89/Voyage 200/TI92 Plus, CAS and Symbolic Math Guide, Graphing Calculator Comparisons, Derive, muLISP, TI
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 Discussion of Block Scheduling  Kidsphere K12 Mailing List
Dan Johnson, a teacher, describes block scheduling in his school: over 90% of faculty and students favored the new schedule. Discussion of some advantages and disadvantages.
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 Discussions  Math Forum
The Math Forum's discussions include mathematics and math educationrelated newsgroups, mailing lists, and Webbased discussions. Read recent and older messages, find out how to subscribe to a mailing list that interests you, read an MAA Online article
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 Disfruta Las Matemáticas  Rod Pierce, mathsisfun.com
Spanish language version of Maths is Fun.
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 DISME: The Art of Tenths  Simon Stevin
Definitions appertaining to Arithmeticall whole Numbers. Decimall arithmetike, Teaching how to performe all Computations whatsoeuer, by whole Numbers without Fractions, by the foure Principles of Common Arithmeticke: namely, Addition, Substraction, Multiplication,
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 Dissections: Plane & Fancy  Greg Frederickson, Cambridge University Press
A book that explores an area of mathematical recreations, called geometric dissections, or the cutting of one or more figures into pieces that can be rearranged to form other figures. With an emphasis on using as few pieces as possible, these geometrical
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 Distance Calculator Between Cities  Dan Gallagher
Enter two cities or countries and this CGI illustrates them on a scaled political map, calculates the distance between the two locations in miles and kilometers, and provides information about latitude, longitude, bearing, and airports. All latitude and
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 Distance, Rate, and Time  Math Forum, Ask Dr. Math FAQ
Distance = Rate x Time: A discussion and two problems.
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 Distance Recipe (Geometry and the Imagination)  Conway, Doyle, Gilman, Thurston; The Geometry Center
A technical definition of how to compute distance. Examples of distances; The Unit Disc Model; Passing from one model to another...
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 Divide!  Andrew Starr
A web page used to demonstrate that if you divide any two integers, eventually the decimals will repeat.
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 Dividing 12foot Boards  NASA Lewis Learning Technologies Project
Lewis needs 1,500 boards to build a small rocket. Each board must be 3 feet long. If boards are sold in 12 foot lengths, how many boards must Lewis buy and cut into 3 foot pieces to get the 1,500 he needs? A detailed answer is provided. From NASA's 9th
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 Dividing by 0  Math Forum, Ask Dr. Math FAQ
Why can't you divide by 0? Why is 0/0 "indeterminate" and 1/0 "undefined"? Why is dividing by zero "illegal"?
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 Dividing Decimals  NASA Lewis Learning Technologies Project
Dividing decimals: What is 12.8 divided by .04? A detailed answer is provided. From NASA's 9th Grade Math Proficiency Test.
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 Dividing: Fractions and Mixed Numbers  NASA Lewis Learning Technologies Project
What is 1 1/2 divided by 1/2? A detailed answer is provided. From NASA's 9th Grade Math Proficiency Test.
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 Dividing Fractions  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about dividing fractions, including an explanation of the "invertandmultiply" rule.
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 Dividing Fractions  Math Forum, Ask Dr. Math FAQ
How do you divide fractions? Say, 2/3 divided by 3/4.
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 Dividing The Plane  Jim Loy
A line divides the plane into two pieces (regions). Draw another line. The plane is now divided into three or four regions. It is three regions if the lines are parallel, four if they intersect. A third line divides the plane into seven regions. Find
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 Divisibility Rules  Calculation Tips & Tricks, The Math Forum
Tips for figuring out whether a number can be divided by the numbers 313, with a Spanish translation and an explanation of why the rules work by Robert L. Ward.
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 Divisibility Rules  Math Forum, Ask Dr. Math FAQ
How can you tell whether a number is divisible by another number (leaving no remainder) without actually doing the division? Why do 'divisibility rules' work?
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 Divisibility Rules to 50 and Beyond  Stephen D.T. Froggatt; Math Forum, Ask Dr. Math FAQ
A quick way of testing primality of larger numbers: the idea of deleting the last digit and adding or subtracting a multiple of the digit from the remaining number can be generalized to test for divisibility by prime numbers up to 50 and beyond.
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 Divisibility War  Diane Reed
A game designed for secondary level students studying basic mathematics to use the divisibility tests to determine whether a number is divisible by 2, 3, 4, 5, 6, 9, and 10.
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 Divisible by 3  Andrew Stadel
Stadel has taught prealgebra, algebra, and geometry in middle school since 2004. His blog about "interactions with math, logic, life, teaching, and the web they spin together" dates back to March, 2012, with posts such as "Survey your students"; "2012
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 Division by Zero  Dave Richeson
A blog about "math, puzzles, teaching, and academic technology." Posts, which date back to September of 2008 and sometimes introduce original applets, have included "Volumes of ndimensional balls," "Albrecht Dürer's ruler and compass constructions,"
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 Division with Roman Numerals  Jim Loy
Roman numeral division can be very easy or fairly difficult, depending on the two numbers. An example of division by pieces, and a general method using repeated subtraction.
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 Divisor Plot  Jeffrey Ventrella
"We hear of primes described as the 'building blocks' of all numbers. Let's turn that concept on [its] head. Instead, let's think of primes as the negative spaces behind complex objects. Imagine a series of picket fences stacked in front of each other.
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 DIY Calculator  Clive (Max) Maxfield and Alvin Brown
Order the book How Computers Do Math, or preview its table of contents. The book's interactive laboratories guide you in the creation of a simple calculator program to run on your DIY Calculator; its accompanying CDROM contains a virtual "DoitYourself
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 DLK MathsWork Software
Selfdifferentiating, topicspecific math software for Windows 3.1 and above, on number, shape and space, and data handling. All of the practice modules have on screen monitoring at three levels. Six problem modules designed to improve users' application
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 DO MATH...and you can do anything!  National Council of Teachers of Mathematics (NCTM)
Features grade levelspecific mathematical activities that children can do with their families and on their own, as well as links to other sites where children can explore the connections between math and some possible career paths. Also includes a family
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 Domebook  Tom Camilli
Cardboard and transparent plastic geodesic domes built by children. Students start by constructing paper models, then apply scale factors to construct domes of any size using cardboard or wooden dowels and plastic sheeting. See pictures of classroom projects;
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 Dominoes Activity  Suzanne Alejandre
A classroom activity (similar to Pentomino + 1 = Hexomino; a variation on polyominoes) aligned to the NCTM and California Standards, to be explored through manipulatives (paper dominoes). Students explore whether it is possible to cover a 6x5 grid with
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 donalduncan's Channel
Narrated paper and pencil instructional videos  some, specific to British Columbia's Foundations of Math and Precalculus exams  on number, line segments and lines, rational expressions, factoring, quadratic functions, functions, exponents, polynomials,
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 Don't Hate No Math  Elio Motella
Advice for students, parents, and teachers. The document called "Lecture" includes sections such as "The causes of your troubles," "It's called metacognition," and "Mental models and propositional representations"; see in particular Part D, titled "An
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 Doodal  Neil Thapen
Draw fractals freehand using a computer mouse: select a "brush size" to specify width in pixels, then click and drag in the large orange frame, the contents of which get copied in however many blue frames you specify. To rotate a blue box, click it while
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 Dositey.com  Dositey Corporation
Interactive lessons, exercises and worksheets, educational games, openended questions in Math and Language Arts, and more.
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 Doubling Pennies  Math Forum, a Classic Problem from the Ask Dr. Math FAQ
Which is more, a million dollars or a penny doubled every day?
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