 Truel in the Sun  Ivars Peterson (MathTrek)
Brilliant sunshine bakes a huddled row of ramshackle, weatherbeaten buildings lining a dusty thoroughfare. Two gunfighters slam out of a decrepit saloon and stalk toward their posts at either end of the street. Facing each other, they prepare to draw
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 The Truth Tree's Math and Logic Board  Bob Scott, Ron Savori
A collection of math and logic problems, from Pascal's Pizza Parlor and Leaning Ladders to The Old Lady and the Eggs and The Rickety Table Disaster. Register to solve these and other problems and compete with other visitors to The Truth Tree.
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 Tumblehome Learning
Makers of educational products such as Lost in Tangrams and  through a partnership with TERC, with funding from the National Science Foundation (NSF)  Mixing in Math (MiM) cards, gameboards, and books.
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 TurnOnCCMath.net  Confrey, Jere, et al.
Learning trajectories that unpack the K8 Common Core State Standards (CCSSS) for Mathematics from the standpoint of student learning, and elaborate the underlying scientific research in mathematics education. Click on a hexagon or a trajectory for detailed
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 Tutor.com  Tutor.com, Inc.
Onetoone realtime help from professional subject experts and librarians. Students looking for homework help may check if their local library or afterschool center offers free tutor.com tutoring; try tutor.com personal online tutoring free for a week;
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 Tutor For Maths  Vikram Singh
Onetoone math tutoring, consulting, brainstorming, and editing sessions conducted online while on the phone with WhizIQ electronic whiteboard software.
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 The Tutor House: math  Adrianne Meldrum
Tutoring elementary and middle school students, Meldrum would often "hunt the Internet for tips and helps on teaching concepts to my students. I find great stuff, but I wanted somewhere central that other tutors like me could find them...." Every Wednesday
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 The Tutorials Search Engine
Searchable listings of tutorials on a variety of subjects, including mathematics.
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 Tutoring Unlimited  Roman Chertes
Math assistance for local students in Stamford, CT. Information about the tutor and services offered.
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 TutorIT Math Skill Tutors  Intelligent Micro Systems, Ltd's (DBA Scandura)
Adaptive tutorials that identify what a math student does and does not know  and then provide the information needed by that student to master the skills taught. Packages include basic facts (addition, subtraction, multiplication, division), algorithms
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 TutorLinker: The Most Innovative Tutor Network  TutorLinker.com
TutorLinker uses online map system so people who are looking for local tutors can easily find their location and compare with other tutors. All services are currently free.
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 TutorMatch  TutorMatch.com
A tutoring referral service for educators and students. Professional and skilled tutors offer academic assistance and skills development, geared to the learning styles of their students. Tutoring options include face to face meetings or individualized
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 TutorNEXT  tutorNEXT, Inc.
Oneonone, individualized tutoring sessions in math and English. An enrichment program in math, and free printable math worksheets, are also available. Full listing of services on the site.
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 Tutor Pace  Tutorpace Inc.
Online homework help tutoring. Free math resources include descriptions of and primers for prealgebra, algebra, geometry, trigonometry, statistics, and calculus.
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 TutorTeddy.com
Online tutoring sessions across grades in arithmetic, algebra, statistics, probability, calculus, geometry, and trigonometry. The TutorTeddy.com site also freely offers more than a hundred chalkboard video lectures and worked problems.
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 TutorVista  TutorVista.com
Interactive lessons, worksheets, and homework help for math students grades 312 from this online education company.
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 Tutor World Online
This online tutoring service sells homework help and SAT preparation packages. The Tutor World Online journal posts free primers in math.
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 TuvaLabs  Tuvalabs LLC
Common Corealigned math learning units based on "topics, news stories, and significant events occurring in student's life outside school," such as sports and nutrition.
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 TuxBlocks  Thomas Price
Click and drag colorful block representations of constants and coefficients from one side of the equation to the other, step by step, to isolate the variables and solve the algebra problems. Points earned through such diagramdriven, mouseonly algebraic
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 Tversky's Legacy Revisited  Keith Devlin (Devlin's Angle)
"Amos Tversky died earlier this year. To mathematicians, the Stanfordbased psychologist is best known for the research he did with his colleague Daniel Kahneman in the early 1970s, into the way people judge probabilities and estimate likely outcomes
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 Twenty Tosses (TEAMS)  Jeannie Toshima; TEAMS Distance Learning, Los Angeles County Office of Education
Toss a coin twenty times, and share class results. Students predicted how many heads or tails they might get if they toss a coin 20 times; tossed coins 20 times and recorded their results; compared their predictions with the actual results; teachers collected
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 Two Equals One?  Jim Loy
A proof that 2=1, what's not "legal" about it, and a discussion of infinity.
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 The TwoHeaded Quarter by Joseph Ganem  Chartley Publishing, LLC
A companion site to The TwoHeaded Quarter, written by a physicist scrutinizing daytoday financial decisions, such as "How far should you drive to buy cheaper gas?" and "Is money saved when you buy on sale?" and "How far should you drive to save money?"
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 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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 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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 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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 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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