 Dear Marilyn, About Leap Years (Math Chat)  Frank Morgan, MAA Online
Your explanation [in Parade Magazine] of September 13, 1998 that we may need to skip a leap year EVERY FEW THOUSAND YEARS because the tropical year (about 365.2422 days) is a bit shorter than the average calendar year (365.2425 days) neglects CHANGES
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 Decibels (Math Chat)  Frank Morgan, MAA Online
Challenge: The Christian Science Monitor of July 8, 1999, reports that "according to the NRDC, the amount of ambient noise in the ocean may have increased by 10 decibels  in other words, 10fold  between 1950 and 1975." Is this correct?
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 Decimal Coins of the UK  Tony Clayton
The change to decimal coinage: Decimalisation Day. DDay was February 15th 1971. On that day the United Kingdom changed from the centuries old tradition of using 12 pence to the shilling and 20 shillings to the pound to a new decimal 100 new
pence to
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 Decimal numbers (Middle School Math)  Homeworkhelp.com, Inc.
A lesson on decimals: What is a decimal number? Converting fractions to decimals, and decimals to fractions; Adding and subtracting decimal numbers; Multiplying decimal numbers; Dividing decimal numbers; Rounding.
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 Decimal Places on a Number Line  NASA Lewis Learning Technologies Project
Decimal places: On a number line, which of the following numbers would be the farthest to the right? 0.001, 0.0015, 0.00099, 0.0005. A detailed answer is provided. From NASA's 9th Grade Math Proficiency Test.
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 Decimals and Logarithms in the Works? And a Dyer's Hand too?  Penn Leary
Shakespeare, Decimals and Logarithms: What did Shakespeare know about mathematics, particularly logarithms and the decimal system? And when did he know it? An article partly from Leary's book, The Second Cryptographic Shakespeare.
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 Decision Analysis Society (DAS)  INFORMS
DAWeb promotes the development and use of logical methods for the improvement of decisionmaking in public and private enterprise. Such methods include models for decisionmaking under conditions of uncertainty or multiple objectives; techniques of risk
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 Decision Development Corporation
Software for K12 students and teachers, for all platforms. Math software included separately and as part of other product lines. (Gigamath Playground and Junior Gigamath Playground offer word problem practice for ages 714 and 48 respectively; Ellen
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 Decisioneering, Inc.
Excelbased decision analysis software tools (Crystal Ball, CB Predictor) for risk analysis and business forecasting.
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 Decision Making Information  Model Education Systems Associates: MESA, Inc.
MESA specializes in the development, implementation and use of decision support systems and related quantitative information resources, especially quantitative tools for research, evaluation and policy analysis directed toward children and their living
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 Decision Sciences Institute
An interdisciplinary, international organization dedicated to the advancement of the science and practice of education and research about business decisions. Publishes the Decision Sciences Journal.
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 Decision Theory and Decision Trees  Mind Tools
A method for organizing and analyzing financial decisions, and other decisions with clear numerical payoff.
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 Decision Tree for Optimization Software  Hans D. Mittelmann, P. Spellucci
Information on optimization software and optimization research, including links to a dictionary, tutorials, testcases, interfaces, and software.
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 Deckulator  Michael B. Moore
For your collectible trading card games, especially Magic: the Gathering. Deckulator calculates the percentage that a card combination will occur in the first cards dealt off the top of the deck. The calculator uses multivariate hypergeometric distribution.
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 Deep in the Jungles  Ivars Peterson (MathTrek)
Humans are predisposed to seeing order and meaning in a world that too often presents random choices and chaotic evidence. Random events sometimes get linked into a meaningful, though ultimately bogus, scenario... At the same time, the mathematics of
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 Deepwater Horizon Incident  The National Oceanic and Atmospheric Administration (NOAA)
NOAA has put together a site full of resources about the Deepwater Horizon oil spill in the Gulf of Mexico. In the left margin, choose "Information for: Students and Teachers" to access data sets as well as articles for the classroom, such as a Q&A that
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 Defending the Roman Empire  Ivars Peterson (MathTrek)
Questions of military strategy can be handled mathematically. Charles S. ReVelle of Johns Hopkins University in Baltimore and Kenneth E. Rosing, recently retired from Erasmus University Rotterdam, describe their approach in the AugustSeptember American
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 Defining Geometric Formulas (Ask Dr. Math FAQ)  Math Forum
Definitions of two and threedimensional figures in general, and a note on dimensions.
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 The Definitive Four Fours Answer Key  David A. Wheeler
From 0 up to 40,000, whole number mathematical expressions that use only common mathematical symbols and exactly four 4s. Wheeler offers his solutions in three different formats: an abbreviated list of answers; a text file of results, mathematical expressions,
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 Dekov Software
Educational software, a journal of computergenerated Euclidean geometry, and a computergenerated encyclopedia of Euclidean geometry. Current software titles include: Solving Triangles (stepbystep solutions to triangle problems in elementary geometry);
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 Delaware State Data Center  Delaware Economic Development Office
A focal point for the distribution of census information in Delaware and for the dissemination of other information from the federal government, state government and other sources, coordinating the use of census and other data for economic development.
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 Deliberative Discourse Idealized and Realized: Accountable Talk in the Classroom and in Civic Life  Sarah Michaels, Catherine O’Connor, Lauren B. Resnick
An article in PDF format. Abstract: Classroom discussion practices that can lead to reasoned participation by all students are presented and described by the authors. Their research emphasizes the careful orchestration of talk and tasks in academic learning.
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 Delphi For Fun  Gary Darby; Intellitech Systems Inc.
Delphi is based on the Pascal programming language developed in the early 1970s by Niklaus Wirth and named after mathematician Blaise Pascal. This site explores the use of programming as a tool in math problem solving, discussing interesting problems,
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 Delta Blocks  Hop David
A way to model different 3D tessellations and a tool for studying geometry, crystallography, and polyhedra. Delta blocks were inspired by M. C. Escher's print "Flatworms," which he said demonstrates that one can build a house not only with the usual
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 Demiregular Tessellations  Totally Tessellated
Color renditions and a real example of a demiregular tessellation. Templates allow you to print renditions of each tessellation suitable for coloring activities.
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 Demography: the Java Version  Daniel Udovic, Joshua Coxwell
Java Demography 2.0.2 simulates growth in age structured populations. The program's click and drag features allow users to directly manipulate the fertility and mortality graphs and the population's current age distribution, represented as a bar chart
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 De Moivre's Theorem  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about de Moivre's theorem, including its usefulness and proofs.
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 The De Morgan Journal  London Mathematical Society
The De Morgan Journal aims "to encourage academic mathematicians to reflect on current issues in mathematics education at all levels, from primary school to graduate studies; to encourage them to explore links between higher mathematics and elementary
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 Demos with Positive Impact  David R. Hill and Lila F. Roberts
Demos with Positive Impact organizes effective math teaching tools. Submit your own demo, or browse the existing collection of physical demos, calculator demos, databased demos, browserbased demos, and software demos, each with statements of objectives,
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 Demos with Positive Impact  David R. Hill and Lila F. Roberts
A collection of classroom demonstrations that use some form of instructional technology. The authors invite others to submit demos and provide them with feedback on the demos already collected. Demos are organized under the levels of Pre Calculus, Calculus
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 Dennis Stanton
Dennis Stanton is a professor at the University of Minnesota studying combinatorics and hypergeometric functions. Many of his papers are available online in PostScript and PDF formats. There are also exams and solutions from previous classes, and a complete
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 Density Functional Theory in Hydrodynamics
Density functional theory in hydrodynamics of a multicomponent multiphase
mixture. Density functional theory describes the multicomponent multiphase
mixture continuously without density jumps and interfacial surfaces.
Bulletin /Field of Application/
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 Departamento de Didáctica de la Matemática  Universidad de Granada
The University of Granada's Department of Mathematics Instruction features research groups, each with bibliographies of downloadable publications and other resources, on numerical thinking (pensamiento numérico), statistics education (educación
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 The Department of Applied Science Wavelet Group  Lawrence Livermore National Laboratory
The Wavelet Group is interested in studying the use of the wavelet transform in the solution of various types of problems. The primary area of current study is Signal Processing Using the Wavelet Transform Electrocardiogram (ECG). People, recent papers,
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 Department of Logic  Faculty of Philosophy, Moscow State University, Russia
In English and Russian. History of the department, staff, books, papers, courses, news.
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 Department of Mathematical Sciences  U.S. Military Academy, West Point
Publications include Cryptologia, CASE (Computer Algebra Systems in Education), Mathematica Militaris, and PRIMUS (Problems, Resource, and Issues in Undergraduate Mathematics Studies). MathTECH is a research project that provides Java applets and TI89
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 Department of Mathematics and Computer Science  North Carolina School of Science and Mathematics (NCSSM)
Learning materials for teachers and students include resources on algebra, advanced functions, and mathematical modeling; data sets used with the NCSSM textbook Contemporary Precalculus Through Applications; the AP Calculus Web Center; and Mathematics
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 Department of Science & Mathematics Education: Research and Development  Univ. of Melbourne, Australia
Read faculty research and learn about their projects and interests: children's understanding of statistical and probabilistic concepts; the negotiation of meaning in mathematics & science classrooms (The Classroom Project); the expression of algorithms
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 Dept. of Statistics  University of Illinois at UrbanaChampaign
Web pages generated by statistics courses; biographical sketches of faculty, staff, lab members, and graduate students; department newsletter. Graduate program admission requirements, degrees offered, courses, statistical consulting services, and The
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 Derek's Daily Math  Derek Orr
"Every Number Has a Story to Tell." This blog by an undergraduate at the University of Pittsburgh details number theoretic properties for every day of the calendar year. Orr, a physics and math major, also maintains a list of "Interesting Propositions/Theorems
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 Derivations of Applied Mathematics  Thaddeus H. Black
An opensource book on the essential ideas underlying the derivations of a large number of mathematical results useful in the modeling of physical systems. PDF, with LaTeX source available under the GNU General Public License.
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 Derivative and Integral  Bill Finzer, Key Curriculum Press
Two sketches demonstrating elementary calculus concepts. Each sketch shows the graph of a function and the graph of its derivative. One sketch lets you change the graph of the function and watch the effect on its derivative. The other sketch lets you
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 Derivative Calculator  David Scherfgen
Compute derivatives of functions online, for free. Supporting symbolic computation of the 1st, 2nd, and subsequent derivatives of multivariable functions, the Derivative Calculator dynamically typesets expressions while you type them. derivativecalculator.net
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 Derivative  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about derivatives, from definitions and explanations to alternate forms of the derivative formula.
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 The Derivative Project: Using Appropriate Technology to Teach the Concept of Derivative Via a Graphical Approach  Lisa Denise Murphy
Murphy has developed an instructional unit that uses a motion sensor and related software to introduce the concept of a derivative, and tested it in a firstsemester calculus class, with very good results. She is now engaged in expanding this project
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 Derivatives Page  Financial Pipeline
Derivatives are financial securities whose value is derived from another "underlying" financial security. Options, futures, swaps, swaptions, and structured notes are all examples of derivative securities. Derivatives can be used in hedging, protecting
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 Derive  Texas Instruments, Inc.
DERIVE software is a Computer Algebra System (CAS) for personal computers (Windows, DOS). In addition, the CAS technology in DERIVE is incorporated in TI89 and TI92 calculators. Derive applies the rules of algebra, trigonometry, calculus, and matrix
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 Desafios Matemáticos  Paulo Ferro
Cinco desafios novos cada mês. Ferro, um professor de matemática licenciado pela Universidade de Coimbra, tambem oferece demonstracões de geometria dinâmica, jogos matemáticos, biografias de matemáticos, exames
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 Descartes 3  Ministry of Education, Culture, and Sport, Spain
Create interactive math lessons in web page format with this applet, or download any of more than 60 already created applets (ranging from "representing numbers on a straight line" to "tables and algebraic terms," from "geometry and a game of billiards"
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 Descartes' Formula (Geometry and the Imagination)  Conway, Doyle, Gilman, Thurston; The Geometry Center
The angle defect at a vertex of a polygon was defined to be the amount by which the sum of the angles at the corners of the faces at that vertex falls short of and the total angle defect of the polyhedron was defined to be what one got when one added
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