 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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 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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 Domino Artwork  Robert Bosch
Mathematical artwork of Bosch, who uses optimization techniques to create domino mosaics, flexible Truchettile mosaics, mapcolored mosaics, Traveling Salesman Problem (TSP) art, simpleclosedcurve sculptures, loops, labyrinths, and more. A professor
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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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 Doubling the Cube  MacTutor Math History Archives
Linked essay covering the history of and some solutions to the classical
problem in Greek mathematics of doubling or duplicating the cube, also called the
Delian problem; and on proving the impossibility of constructing a solution using only ruler
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 Downloads  Mac  Mathematics  CNET Download.com
Search this site to find a particular piece of software for the Mac, or browse their mathematics listings.
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 Downloads  PC  Mathematics  CNET Download.com
Search this site to find a particular piece of software for the PC, or browse their mathematics listings.
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 Do You Know That...  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
A collection of short essays about over 60 curious mathematical facts and terminology, mostly linked to explanatory or exploratory essays, drawn from various parts of Bogomolny's site, CuttheKnot. See page two and page three.
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 Do Your Home Work Arizona  Stand for Children Arizona
A free tool for Arizonan parents to better understand the homework assigned to their children. Use the pulldown menus to select math and a grade K8, or search with a keyword, for outlines of math content standards, homework help resources, and access
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 A Dozen Reasons Why Schools Should Avoid Filtering  From Now On (FNO)
Why schools should not block access to particular sites: filters may not work very well;. they may work too well; they may increase attention to SMUT and spur motivation; their ongoing cost may block better programs from your students; they may create
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 DPGraph (Dynamic Photorealistic Graphing)  David Parker
Software that allows you to: display multiple simultaneous dynamic photorealistic 3D implicit equalities and inequalities, and intersections of their volumes; spin, slice, and view timedependent (moving) photorealistic surfaces in real time; and construct
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 Dr. Aardsma's Math Drill  Aardsma Research and Publishing
Commercial computer software for giving automatic flashcardstyle math facts drills to elementary students. Drills addition, subtraction, multiplication, and division.
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 DragonBox  WeWantToKnow AS
"Secretly teaching algebra to your children" by letting them discover algebraic rules, play with them, then use the rules to solve puzzles through trial and error. See testimonials and videos about this multiplatform math game created by WeWantToKnow
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 Dragonfly Web Pages  Miami Univ. of Ohio with the NSTA
Dragonfly is an inquirydriven magazine published bimonthly during the school year, inspiring children to join with their peers and with scientists in national and international investigations. Dragonfly also publishes poetry, autobiographies, natural
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 Dr. Alfred Posamentier  Education Update, Inc.
Blog by the Dean of Education at Mercy College (New York). Posamentier's Posts, which date back to August, 2010, have included "A Power Loop," "The Unusual Number Nine," "The Irrepressible Number 1," "Enriching Mathematics Instruction, Rather than Teaching
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 Dramatic Results
This nonprofit educational arts agency improves students' academic confidence and performance "by stimulating curiosity and fostering creativity through a handson, artsbased approach to learning." Dramatic Results specializes in curriculum that integrates
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 DreamCalc for Windows  Andy Thomas
A freeware scientific calculator for Windows, intended to replace standard handheld calculators. Fully featured range of math, scientific, statistical & financial functions. Supports natural fractions, complex numbers, basen logic, unit conversions
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 Dream Frequency .com
CGI web applications to calculate the factors of a number, calculate the prime numbers below a number, test a number for primality, calculate a word's position in the alphabetically sorted list, convert hex to ASCII, or convert temperature from celsius
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 Dream Home Mathematics (SMILE)  Dennis W. Montgomery, Lyman Trumbull Academy
A lesson for grades 512, designed to teach students to use basic math to determine affordability of a home based on a given income; calculate decimal placement for currency, percentages and interest; estimate affordability based on income; investigate
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 Dr. Freemath  Bob Pawloski, Office of Internet Studies, University of Nebraska  Omaha
Archives of a project where elementary classes asked mathematics questions of the Omaha FreeNet, Project TEAM Internet (UNO), and the Technology Task Force of the Eastern Region Math and Science Coalition. Questions and answers range from "At the speed
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 Dr. Genius  Hilaire Fernandes
Dr. Genius: "Geometry Exploration and Numeric Intuitive User System." The successor of the Dr. Geo Project, this GNU interactive geometry software allows the construction and manipulation of geometric figures. Read documentation, subscribe to the mailing
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 Dr Lamin Tutor Books
Free programs on CDROM, produced by Dr S.M Hajsadr (you must pay postage and
packaging if you find them useful). Essential Maths is the first in a series of Tutor Books that aim to make learning mathematics easy and consistently planned. Topics include:
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 Dr. Math Books  the Math Forum @ Drexel
Featuring Internet references, glossaries, indexes, illustrations, and questions written by actual kids, each can be purchased from Amazon.com via links on this page. The page details the contents of each book: Dr. Math Gets You Ready for Algebra, Dr.
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 Dr Mike's Math Games for Kids  Michael Hartley
Free printable and online math games for kids: traffic jam, times tables, magic square, magic hexagon, sugar sugar, Archimedean tilings, magical calculator birthday trick, and more. Newsletters include Monday Morning Math, with what math says about daily
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 Dueling Pinwheels  A Geometer's Sketchpad Activity  Cynthia Lanius
Construction directions for rotations, translation, and reflection, with questions to explore and a demonstration sketch to download.
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 Dynamic Geometry  Goldenberg, Scher; Education Development Center, Inc.
To understand how students construct mathematical ideas in "Dynamic Geometry" environments (tools like Geometer's Sketchpad and Cabri), one needs clear characterizations of the mathematical "raw materials" embodied in the software and how students use
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 Dynamic Mathematics Visualization for Young Learners
Sketchpad in Grades 38  a working conference, held at the University of Illinois at Chicago in February, 2003. Researchers, curriculum developers, and educators began developing a curriculum and software structure around The Geometer's Sketchpad technology
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 Dynamic Number  KCP Technologies, Inc.
Classroomready activities of The Geometer's Sketchpad® for interacting with mathematical objects to develop deep understanding of number and early algebra concepts. Some of this content received support from the National Science Foundation (NSF)
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 Dynamic Web Tools Using webMathematica  Steve Wilson and Mike Martin, Johnson County Community College, Kansas
Interactive Web pages that allow students and faculty to compute and visualize mathematical results directly from a Web browser. Primarily for undergraduate courses, the pages are grouped by categories and a given page may be listed under several categories
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 Dynamische Geometrie Systeme (DGS)  Dr. Dörte Haftendorn
In German. Characteristics and comparisons of dynamic geometry systems; Euklid: characteristics, material, notes, software, lessons; TI92 calculator Cabri Geomètre materials. You may send for a 40page booklet on "Dynamic Geometry of Systems"
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 Dyscalculia and Maths Difficulties  Learning Works International Ltd
Conferences, teacher courses, in service educational training opportunities, research, and more from the publishers of Working with Dyscalculia.
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 Dyscalculia.org  R. M. Newman
Learn about dyscalculia: definitions, cognitive research, symptoms, diagnosis and best practices, classroom techniques, home learning aids, legal questions, papers such as "Developmental Perspectives on Dyscalculia: Implications for Teaching in the Middle
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 Dyslexia  George Row
A compensium of links to other WWW pages and discussion groups on Dyslexia: basics, organizations, bibliographies, archives, software, research; also special needs education in general; and pointers to general disability information.
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 Dyslexia Online
An online magazine offering information on and resources for dyslexia.
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 Dyslexia Symptoms & Dyslexia Signs  Benetta Strydom
A resource on the symptoms of dyslexia, including the possible effects of
this disorder on math and handwriting.
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 Eagle Geocoding  ETAK, The Digital Map Company
Input an address and the Eagle Geocoder will return the following data: full Zip Code, latitude and longitude, County, Urbanized Area Code, Population Density, Minor Civil Division, Place, Tract, and BlockGroup. You may also request a map with the address
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 Earliest Known Uses of Some of the Words of Mathematics  Jeff Miller, Gulf High School, New Port Richey, FL
An extensive list, with examples, sources, and contributors. These pages attempt to show the first uses of various words used in mathematics. Research is ongoing, and the uses cited should not be assumed to be the first uses that occurred unless it is
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 Earliest Uses of Various Mathematical Symbols  Jeff Miller, Gulf High School, New Port Richey, FL
An attempt to identify the individuals who introduced various common mathematical symbols, along with the dates and name of the document in which the symbol first appeared: symbols of operation; grouping symbols; symbols of relation; fractions and decimals;
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