 Two Trains  Math Forum, a Classic Problem from the Ask Dr. Math FAQ
Two trains leave different cities heading toward each other at different speeds. When and where do they meet?
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 Tying Down a Random Walk  Ivars Peterson (MathTrek)
For many men, the ordeal of fashioning a neat tie knot is fading into the distant past. It seems ironic that two physicists have now put necktie knots back on center stage. Thomas M. A. Fink and Yong Mao of the Cavendish Laboratory in Cambridge, England,
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 Typing Math  Math Forum, Ask Dr. Math FAQ
How should I type exponents? What about square roots? Why not use tabs? May I send attachments?
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 UCALC  Daniel Corbier
Windows shareware tools to compute compound interest, convert from miles to kilometers, solve a quadratic equation, plot a 3D surface, or simply add up bills. Features include: Expression Evaluator (evaluates expressions such as "5+4*1013"); Unit Converter;
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 UC Museum of Paleontology  University of California at Berkeley
Online exhibits, education and outreach programs, catalogs and collections, and links to other science and museum sites. Paleontology incorporates many different kinds of data from different fields. Search for type specimen data from the museum's Catalogs
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 UCSB Department of Mathematics Center for Mathematical Inquiry  Regents of the University of California
Developing "inquirybased learning approaches in the teaching of mathematics and a research base that examines teaching and learning through inquirybased practices." See past workshops, course materials for University of California Santa Barbara (UCSB)
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 UK Mirror Service  Joint Information Systems Committee, Higher Education Funding Councils, UK
Formerly HENSA, this national software archive service benefits the higher education and research community in the UK, funded by the Joint Information Systems Committee of the Higher Education Funding Councils. It maintains copies of electronic archives
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 The Ultimate Puzzle Site  van Gassel, Heijmans, van Veldhoven
A site in English and Dutch by three Dutch students. Contents include: Various Basic Puzzles and Riddles (no mathematics); Harder Puzzles and Riddles (no mathematics); Mathematical and Logicdeductional Puzzles with solutions; BrainTeasers; and Complex
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 ULTRALAB  Anglia Polytechnic University, U.K.
A research centre that writes software for learners of all ages and researches all aspects of the use of technology in learning. Reports, papers, and articles; 'old' software and hardware computing archive.
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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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 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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 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 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 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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 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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 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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 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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 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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 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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 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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 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 Math Solver  Stanislav Kublanovsky
Software that solves problems of arithmetic, algebra, trigonometry, calculus, and other mathematics. Graphs, tables, and automated verbal and written commentaries — also available in French, Russian, Dutch, German, Italian, Spanish, and Hebrew —
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 The University of Chicago School Mathematics Program (UCSMP)
A K12 curriculum begun in 1983, with educational materials designed to bring the real world into the classroom, emphasizing reading, problemsolving, everyday applications, and the use of calculators, computers, and other technologies. Unnecessary repetition
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 Unlocking Ways to Make Your Math Simple  Rajinder Goswami
An ebook meant to enhance calulating skills. It focuses on comprehension, speed, and accuracy. Two Flash examples provided; download the whole book for a fee.
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 Unlucky in Cards (Math Chat)  Frank Morgan, MAA Online
In his Contract Bridge syndicated column Phillip Alder says that the odds against getting a "Yarborough  a hand with no card higher than a nine" are 1827 to 1, and that the odds against two players getting a Yarborough on the same deal are about 182
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 Unsilence Students' Voices  Suzanne Alejandre
Article discussing how to provide an opportunity for all students to contribute to math classroom discussions. Originally published in the September, 2012, issue of the CMC ComMuniCator, journal of the California Mathematics Council, this article intersperses
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 Untangling the Mathematics of Knots (MegaMath)  Nancy Casey; Los Alamos National Laboratory
Fundamentals of knot theory for a wide range of levels  a variety of activities for exploring knots made from pieces of rope. Students can make and verify observations about knots, classify them, combine them, and find ways to determine if two knots
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 US2020
By organizing a million mentors from industry, this organization hopes to provide "uplifting moments of discovery to children through realworld, handson projects and academic coaching" in science, technology, engineering and math (STEM) fields. The
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 USA Map Jigsaw Puzzle  Jill Britton
Students are challenged to move each of the contiguous 48 states into the correct position on the map. Note the number of colors necessary for separation of the states.
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 U.S. Census Bureau
Information (searchable by keyword and browseable by subject) from summary data files across cities, towns, counties, states, and other geographic and demographic boundaries, useful for many purposes from allocating representation in legislative bodies
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 U.S. Department of Education
Extensive and varied education information in categories including: educational initiatives (President's and Secretary's priorities), funding opportunities, student financial assistance, research and statistics, news and events, programs and services,
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 U.S. Energy Information Administration (EIA)
Links to facts/statistics on energy topics from A to Z: acid rain and air conditioning to world energy data on coal consumption, electricity prices, natural gas and oil consumption, and more. With tables, graphs, articles (some in PDF format), a Windows
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 Usenet FAQ Archive : Recreation : Puzzles  Netmeg Internet
Problems and puzzles, with solutions, from the rec.puzzles archives, in the categories: analysis, arithmetic, combinatorics, competition, decision, geometry, group, induction, instructions, language, logic, physics, pickover, probability, real life, references,
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 U.S. Geological Survey  U.S. Department of the Interior
Scientific factfinding and research organization of the U.S. Dept. of the Interior; the principal source of scientific and technical expertise in the earth sciences within the U.S. Federal Government. Includes The Learning Web, where Teacher Developed
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 Using Children's Literature in Mathematics  Elaine Young
A list of children's books (with authors) that can be used in math lessons.
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 Using Manipulatives  Math Forum, Teacher2Teacher FAQ
Answers to a frequently asked question: What role can manipulatives play in the classroom?
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 Using Symmetry to Create A Community Quilt (SMILE)  Beverly Brown, Hedges West
A lesson for grades 412 designed to teach students about line and reflectional symmetry through cooperative work on a quilt with four lines of symmetry. From the Patterns and Logic section of a collection of almost 200 single concept lessons by the Science
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 Using Technology to Enhance Engaged Learning for AtRisk Students (NCREL)  Barbara Means; Pathways to School Improvement
A "critical issue": An increasing number of educators are calling for high standards and challenging learning activities for atrisk students. New technologies can provide meaningful learning experiences for all children, especially those at risk of educational
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 Using Technology to Support Education Reform  Means, Blando, Olson, Middleton, Morocco, Remz, & Zorfass
1993 publication of the Office of Educational Research and Improvement, U. S. Department of Education. Includes sections on educational technologies, support for student learning activities, support for teacher functions, effects on student achievement,
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 Using the Fibonacci numbers to represent integers  Ron Knott
We use base 10 for written numbers, and computers use base 2, but what about using the Fibonacci numbers as the column headers? or base Phi (1.618034...) instead of base 10? There are some interesting infinite series that relate to these  each with a
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