 Unbreakable Ciphers  Jim Loy
Proving that if the method of encryption is complicated enough, almost any encrypted message can be unbreakable.
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 Uncertain Reasoning Group  Mathematical Logic  Dept. of Mathematics, Manchester Univ., U.K.
Homepage for a research group that investigates uncertain knowledge, how to represent it, and how to reason with it intelligently. People, research topics, seminars, Web resources.
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 Uncle Bob's Puzzles  Robert & Claire Mead, Haverhill, NH, USA
Math and logic problems (no solutions); if you have questions, want a hint, or want to submit a solution you're invited to email the author. Asterisks indicate greater difficulty: Blind Cowboy; A Game of Catch; The Next Three; Grandpa's Birthday; Square
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 Uncle Dan's Algebra Videos  Dan Suttin, Homespun for Homeschoolers
A set of 12 videos plus a CD containing 180page workbook and linebyline solution key. Samples and ordering information available on the site. Uncle Dan offers to email the 180page algebra workbook file as a free gift to anyone who emails him and
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 Uncle Kenny's Mathematics Pronunciation Guide  Kent Kromarek
Billed as a "megametamathematical guide for proper American English
pronunciation of terms and names, for the diacritally challenged," this guide
includes many mathematicians and mathematical terms encountered in high school
and the first two years
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 Uncorking Work Problems (SMILE)  David Drymiller, Marie Sklodowska Curie Metro High School
A lesson designed to teach students to solve problems about work using the formula work = rate x time; to solve equations containing rational expressions; and to strengthen basic skills learned in algebra. From the Practical and Applied Math section of
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 Uncovering Mathematics with Manipulatives and Calculators  Texas Instruments, Inc.
A text that provides K6 activities emphasizing problem solving, reasoning, communications, and connections, clustered into four content strands: number sense; patterns, relations, and functions; measurement and geometry; and probability and statistics.
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 UNdata  United Nations Statistics Division
Search across the UN's statistical databases: education, human development, population, trade, gender, and more. Preview, download, and filter results by sources such as the State of the World's Children (SOWC) and Millennium Development Goals (MDG).
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 Undergraduate Research Project in Random Tilings  Propp, Wilson
This project investigates different regions of random tilings of nxn squares with 1x2 dominoes: square, hexagon, fortress, dungeon, and Aztec diamond (the set of lattice squares completely inside a square tilted 45 degrees, discovering that the dominoes
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 Undergraduates' Page (Mathematics Archives)  University of Tennessee, Knoxville (UTK)
Suggestions and links designed to give undergraduate students information specifically for them. Societies, Undergraduate Projects and Research; Summer Programs, etc.; Competitions; Careers in Mathematics; Undergraduate Publications; Other WWW Sites.
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 Understanding Algebra  James Brennan, Boise State University
In addition to "stuff to play with" on the web (a Graphing Applet (for exploring slope and intercepts of straight lines), a Prime Factorization Machine, a Prime Number List, a Quadratic Equation Solver, and a Quadratic Function Plotter), this book's full
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 Understanding Calculus  Faraz Hussain
An online book that introduces calculus through concepts and engineering applications. Read the illustrated chapters free online, or download the entire work as a PDF for a fee.
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 Understanding Fractions (SMILE)  Florida Bradley, Hartigan School
A lesson designed to teach students to recognize and understand equal fractions in relation to a whole unit. From the Arithmetic section of a collection of almost 200 single concept lessons by the Science and Mathematics Initiative for Learning Enhancement.
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 Understanding (Learning and Mathematics)  Greeno, Riley; Math Forum
In their 1987 article, "Processes and Development of Understanding," James G. Greeno of Stanford University and Mary S. Riley of San Diego State University examine why younger children seem to lack the ability of older children to solve mathematical word
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 Understanding Mathematics: A study guide  Peter Alfeld, University of Utah
A resource and source of encouragement, with questions and Alfeld's comments (Are you frustrated working through heaps of meaningless problems that are all alike? Does the thought "I can look it up if I have to" occur to you frequently? Do you feel that
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 Understanding Mathematics: From Counting to Calculus  Keith Kressin, K Squared Publishing, Inc.
A comprehensive book for anyone who desires clear and concise math explanations, written for a nontechnical audience to cover the math fundamentals normally taught from first grade through college (for more information, see the Table of Contents).
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 Understanding Projective Geometry (Question Corner and Discussion Area)  University of Toronto Mathematics Network
An indepth explanation of projective geometry in response to a high school student's question.
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 Understanding 'Rate' Word Problems  Rick Garlikov
A conceptual explanation of doing various kinds of math "rate" problems (e.g., "distance/speed/time" problems, problems involving combining work done by different agents working at different rates of speed, quantity/proportion problems, etc.).
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 Understanding Temperatures  NASA Lewis Learning Technologies Project
These were the low temperatures recorded for January 15 in these cities: Minneapolis:  6 degrees; Cleveland: 5 degrees; Fargo: 11 degrees; Chicago: 2 degrees; Milwaukee: 3 degrees; Detroit: 1 degree. Which city had the low temperature closest to 0
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 Under the Dome  Mike Wiernicki
Blog by a math coach and a consultant for Learner's Advantage. Posts, which date back to October, 2013, have included "A Number Talks Reflection — A Look Back Over the Past 3 Years ...," "Relevant Decimals Lesson," "The Penny Cube," and "Are Your
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 Undusting Napier's Bones  Alexandros Diploudis; HeriotWatt University, UK
Biographical information about the Scottish mathematician John Napier, generally considered the inventor of logarithms, with a Java simulation of Napier's bones, a method for performing arithmetic operations by the manipulation of rods (called "bones"
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 Une Balade dans le Monde des Polyèdres  Maurice Starck
Les polyèdres convexes, non convexes, et intéressants: les polyèdres uniformes, les stellations de l'icosaèdre, des tétraèdres remarquables, le découpage d'un tétraèdre par un plan, les deltaèdres
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 Unfair Dice  Ivars Peterson (MathTrek)
Dice represent an intriguing example of the interplay between randomness, chance, and physical law. The simplest mathematical model of a standard die is based on the assumption that the die is a perfect cube. A cube has six faces, and each face has an
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 Unfolding Orbifolds  Heidi Burgiel; The Geometry Center
A study of how a pattern can be reconstructed from an orbifold, using both handson exploration and the computer program TesselMania!. These activities are a good introduction to the movie Shape of Space. From Math 5337, Technology in the Geometry Classroom,
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 Unicursal curves and knot diagrams (Geometry and the Imagination)  Conway, Doyle, Gilman, Thurston; The Geometry Center
A unicursal curve in the plane is a curve that you get when you put down your pencil, and draw until you get back to the starting point. As you draw, your pencil mark can intersect itself, but you're not supposed to have any triple intersections. You
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 Unification of System of Linear Equations, Matrix Inversion, and Linear Programming  Prof. Hossein Arsham; University of Baltimore
Remarks on unification of systems of equations, matrix inversion, and linear programming, that is, the links between these topics. Includes references and further reading.
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 UniformMotion Problems: Just Playing With Cars (SMILE)  David Drymiller, Morgan Park High School
A lesson that uses batteryoperated cars to teach students to solve uniform motion word problems using rate X time = distance; and gives them practice in measuring in the metric and English systems. From the Practical and Applied Math section of a collection
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 The Uniform Polyhedra  Roman Maeder
A shortened version of the notebook Polyhedra.ma from Illustrated Mathematics [Gloor/Amrhein/Maeder95]. Uniform polyhedra have regular faces and congruent vertices. Allowing for nonconvex faces and vertex figures, there are 75 such polyhedra, as well
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 Unifpack (Web version 2.0)  Carlos O'Ryan Lira
A set of programs and C libraries for studying Riemann Surfaces with symmetry. Unifpack accepts a presentation of a finite group and calculates the Cayley graph of the group for that presentation. If the presentation is "admissible," Unifpack can calculate
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 Union of Bulgarian Mathematicians (UBM)
A voluntary, creative, nonpolitical organisation whose purpose is to bring together people who are interested in Mathematics and Computer science or are involved in activities related to those fields. Contact info, meetings.
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 Unique Online Math Flash Cards  Lambert Smith, MathRUS.com
Customizable formatting characterizes these flash cards for addition, subtraction, some multiplication and some division. Free 30day trial; afterwards, a subscription is paywhatyoucan. The author writes: "This website for online math flash cards differs
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 Unit Conversion and Day of the Week  Stephen Phillips
Convert between units of distance, area, volume, mass, speed, temperature, pressure, energy, power, or force online, or find the day of the week for a given date. There is also a list of conversion factors for various units, including units of radiation,
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 UnitConversion.org
Perform online unit conversions for volume, distance, temperature, time, speed, and more for a total of 2,100 kinds of units in 78 different categories.
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 Unit Conversions, Unit Cancellation  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about unit conversions and cancellations, from "Convert: 3.25 cm to millimeters...." to "If you can run 100 meters in 10 seconds, how long, in days, hours, and minutes, does it take you to run 12,800,000 meters?"
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 Unit Converter
The converter works for units of area, energy, pressure, volume,
temperature, mass, length, numbers, velocity etc. You put in a number and
select a base unit and select a unit to convert to. The conversion result
will immediately appear in the output
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 Unit Converter
Key in units to convert. Available tabs include area, volume, time, density, length, temperature, moment of inertia, forces, distributed load, bending moment, and section modulus.
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 Uniteasy: Scientific Unit Conversion and Dictionary
The site contains a variety of unit converters, including for space and time (angle, area, length, time, velocity, volume, solid angle, and astronomical distance), electricity, acoustics, chemical, mechanics, magnetism, IT, heat/energy, light, and radiation.
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 The United States and the Metric System  Office of Information Services, National Institute of Standards and Technology (NIST)
A capsule history, with questions and answers, a metric chocolate chip cookie recipe, and some sample size relations (kilogram of butter to pound, etc.).
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 United States Historical Census Data Browser  Paul Bergen
A database on the people and the economy of the US for each state and county from 1790 to 1970. Data include historical census figures and general population characteristics such as "number of free white females," "number of free colored males," and "number
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 UnitJuggler: Online Unit Conversions  Pierre Di Marco
UnitJuggler offers free unit conversions, for distance and length, area, volume, weight and mass, temperature, time, and more.
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 UnitMath Example: Geometric Solids  Paul M. Price
Examples of how to use UnitMath with geometric solids: box (rectangular parallelepiped), cone (right circular), cylindrical solids (can  right circular cylinder; horizontal cylinder, partly filled), oblate spheroid, prolate spheroid, spherical solids
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 UnitMath  Paul M. Price
A calculation utility program for Mac or Windows, designed to answer questions written as equations made up of numbers, units (a unit is a quantity in terms of which the magnitudes of other quantities of the same type can be stated), precision, and operators.
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 Unit Measurement Conversion  NASA Lewis Learning Technologies Project
Which statement is NOT correct? 96 cups = 6 gallons; 9 days = 216 hours; 84 ounces = 7 pounds; 2 miles = 10,560 feet. A detailed answer is provided. From NASA's 9th Grade Math Proficiency Test.
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 The Units of Measure C++ Library  Keith Nicewarner
The purpose of this library is to try to make it more difficult to make
coding mistakes that incorrectly mix units of measure. This is done with a
set of C++ classes that provide typesafe manipulation of units of measure
for various properties.
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 Units of Measurement for Ada  Dmitry A. Kazakov
Public domain software for dealing with physical measurement units. The library provides physically correct unit arithmetic and tools for input and output of units, which including support of various irregular units. As an illustrative example a platformindependent
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 Units of Measurement  NASA Lewis Learning Technologies Project
Which object is matched with its appropriate unit of measurement? Milligrams for the weight of a textbook; Kilometers for the length of a sailboat; Grams for the weight of a needle; Kiloliters for the capacity of a reservoir. A detailed answer is provided.
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 UnitWiz
An online calculator converts units of length, area, density, energy, force, mass, power, pressure, speed, temperature, or volume.
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 Univalg  eGroups, Inc.
Mailing list for use by the Universal Algebra community: subscribe here, or browse archive by month. (Universal Algebra is a technical branch of mathematics related to algebra and model theory.)
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 The Universal Currency Converter  Xenon Laboratories Incorporated
An interactive currency table. Versions are available in English, Spanish, and Swedish. The Universal Currency Converter™ allows you to perform interactive foreign exchange rate conversion on the Internet. Type the amount of source currency in the input
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 Universal Framework for Science and Engineering  Part 5: Category theory  Petr Ivankov
Software for use in Category Theory. The web site describes its function and operation.
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