 Newton's Castle  Steve Feld
Learn about color, optical illusions, how cars appear to roll uphill on "magnetic mountains," why dogs chase cars, and more; then test your learning with the online quiz. Also, see quotations and a timeline of Newton's life. With a bibliography and webliography.
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 NewtonsWindow.com  Suzanne Sutton
For students, families, teachers, and homeschoolers as they learn and teach math. NewtownsWindow.com offers math challenge excursions online, summer learning activities, and educational gifts and ideas. With suggestions for reinforcing concepts at home,
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 New York Group Theory Cooperative at CCNY
Genetic algorithms, open problems and preprints in combinatorial and geometric group theory, meetings, links, and MAGNUS, a free (GPL) graphically oriented system, based on Tcl/Tk, for computational group theory designed to allow for exploration and experimentation
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 New York Regents Exam Prep Center  Oswego City School District
A site dedicated to assisting high school students in preparing for the "new" New York State Math A Regents Examination. Covers Algebra, Geometry, and Algebra II/Trig. The materials featured for each topic include: general review/formula sheet, Regents
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 New York State Regents Examinations/Tests  New York State Department of Education
Tests and scoring keys, listed according to the subject and date administered, provided in Portable Document Format (.pdf). All three levels of Sequential Mathematics, including language editions in Chinese, Haitian Creole, Korean, Russian, and Spanish.
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 Nick's Mathematical Puzzles  Nick Hobson
A collection of puzzles ranging over geometry, probability, arithmetic,
algebra, calculus, and logic. All require ingenuity, but most require only precollege math. Hints, answers, and fully worked solutions are provided, as well as links to relevant
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 Nikoli  Nikoli Co., Ltd.
From the Japanese magazine publishers that popularized sudoku puzzles: the nikoli.com site releases three or more problems every day  more than 100 new problems a month. Step through tutorials and solve Flash puzzles of Slitherlink, Nurikabe, Heyawake,
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 Nim  Doug Ensley, Shippensburg University
Play online: two people play with several piles of stones. On each move a player
removes as many stones as he or she would like, but forms only one pile. The player who takes the last stone wins.
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 Noetic Learning: Your Online Math Learning Center  Li Kelty, Noetic Learning, LLC
Offers a worksheet generator with online publishing capability, in the basic operations and money. See also Noetic Learning's online programs for gifted elementary students, summer enrichment and learning retention, and math contests. Free samples of
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 NonEnglish Math Resources  Math Forum
Students and teachers with NonEnglish language needs will find mathematics and math education Web sites organized by category for the following languages: Spanish, French, German.
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 Nonsexist Solution of the Menage Problem  Bogart, Doyle
A paper that appeared in the American Mathematical Monthly. The ménage problem asks for the number of ways of seating couples at a circular table, with men and women alternating, so that no one sits next to his or her partner. The paper presents
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 North Carolina School of Science and Mathematics (NCSSM) AP Calculus Web Center  John Goebel, Matt Wagers
Available here are postings related to the high school AP calculus program, including a Lesson Center which contains Mathcad® versions of class lectures (Mathcad® 6.0 or later required); Study Aids which provide material useful for AP Calculus exam preparation,
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 The North Carolina State High School Mathematics Contest  John Goebel
Download PDFs of recent contest questions and solutions, and see test statistics and item analysis. Read brief and detailed histories of the contest, rules, and more. The State Mathematics Contest was initiated in 1979 to provide state level competition
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 Northwestern Crows: Using Rational Functions to Investigate the Behavior of Northwestern Crows (iMath Investigations)  Illuminations; National Council of Teachers of Mathematics (NCTM)
An online, interactive, multimedia math investigation in which students use rational functions to explore the possible reasons behind the observation that northwestern crows consistently drop a type of mollusk called a whelk from a height of 5 meters.
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 Northwest to the Pole and TwoHeaded Coins (Math Chat)  Frank Morgan; Christian Science Monitor
Suppose you start at the earth's equator and travel continuously northwest until you reach the North Pole. What does your path look like? How long is your path?
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 The Norwegian Mathematical Olympiad
Problems and solutions from the Abel Competition, the Norwegian Mathematical Competition (NMC), and the Baltic Way, dating back to 1992, many in English. The Norwegian Mathematical Olympiad is organized by the Norwegian Mathematical Society in cooperation
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 Not Just Sums  Emily Hillier, Not Just Sums
Teaching and learning resources from the U.K. Learn about the product range and educational philosophy, and try sample resources, a daily starter activity, and online games.
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 The N Queens Problem  Marty Hall
Finding a solution to the NQueens problem for any N greater than or equal to 4 can be done without searching. Determining where each queen should go can be done in constant time per queen, or O(N) altogether. Thus, drawing the board (which is O(N^2))
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 NRICH Maths, the Online Maths Club  Univ. of Cambridge, UK
A project that aims to establish a permanent national centre for curriculum enrichment to provide mathematical learning support for very able children of all ages. The learning and enjoyment of mathematics are promoted through an Internet Newsletter and
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 Number and Word Puzzles  Ken Egan
Number and word puzzles, including Digicross, in worksheet and interactive (Java) format.
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 A Number Game  Zusheng Rao
Imagine this interesting game. Given 9 numbers (1,2,3,4,5,6,7,8,9), can you make a number like 1997 by using these numbers and +  * operations without changing their positions? This applet can tell you: put 9 in the column corresponding to "Max Number"
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 Numberline Lane  Fiona Cartmell, Nick Reynolds, and Anthony Cartmell
A website accompanying books designed to help teaching and learning math through stories and cartoon illustrations. Meet the residents of Numberline Lane: Walter One, Suzie Two, Hebe Three, Nora Four, Clive Five, Nick Six, Kevin Seven, Katy Eight, Nigel
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 numbermaze  Mike Reilly & Jenks Norwalk
A Sudokulike maze puzzle that uses the number pattern from a clock face, one through twelve. Link these numbers in either direction – clockwise or counterclockwise – through the maze to solve the puzzle. Read complete rules, path strategy, hints, and
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 NumberNut.com  Andrew Rader Studios
Introductions to shapes and colors, counting numbers, addition, subtraction, multiplication, division, order of operations, dates and times, number types, fractions, decimals, percents, estimation and rounding, ratios, money math, factors, graphs and
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 Number Patterns  Harvey Heinz
A brief description of why mathematics is often called the science of pattern followed by examples of a variety of magic squares of various types; examples of orders 5 to 12d magic stars, and selections from Heinz's collection of over 400 number patterns
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 Numberplay  The New York Times
Mathematical, logical and scientific puzzles, with solution "recaps." The posts, by Gary Antonick and Pradeep Mutalik, have included "Surreal Hat Tricks," "The Puzzles of Pickover," "Prime Rib at Hogwarts," "Nim for (a) Change," "Phi  The Magic and the
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 Number Puzzles  Erich's Puzzle Palace; Erich Friedman
Three crosswordgrid style puzzles, with numerical operations filled in. Can you fill in the numbers that work? Answers provided.
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 Number Puzzles  Ken and Dima Boone
Arithmetic puzzles along with hints and answers include "Laying Eggs," "Four Fours Into Seven," "Target Number 278," "Inserting Plus Signs," and "How Many Legs?" and "What's My Number?"
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 Numbers in the World (Math Chat)  Frank Morgan, MAA Online
Select the best occurrence in the world of each number from 1 to 10. For example, 12 is the number of eggs in a dozen or the number of months in a year... with winning reponses. Also: Math Chat has received a number of mathematical jokes, most of them
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 Numbers  Kirsten Silverman
Blog by a Massachusetts middle school math teacher who "loves number theory and thinks sixth grade is the perfect place to share this." Posts, which date back to August, 2012, have included "Flipping"; "Cogs"; "LCM, GCF, and Fractions"; "Ordering Fractions";
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 Numbers Test  Tommie Berry
A Java program for teaching children their math facts. Select the digits and functions (addition, subtraction, multiplication, and/or division) you want to practice, and hit the start button. The applet will generate questions for you, will tell you when
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 Number Strings  Imm, Kara; Lambert, Rachel; et al.
A place to find new strings, post strings, get feedback on design or number choice, and discuss the pedagogy of number strings, a classroom routine based on "sets of related math problems, crafted to support students to construct big ideas about mathematics
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 The Number Years  Libicki, Quinn
A concept originally created by Eric Libicki as a classroom activity to bring a sense of fun to learning the history of mathematics, now in the game show format presented here. Several online versions are available, and users will be able to craft their
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 Numerix Bee  Vel Micro Works Incorporated
A math challenge game designed to develop children's interest, confidence, and fluency in mathematics through solving challenging problems while having fun. Register your school.
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 Nummòlt  Maurici Carbó Jordi
Math teaching resources built by architects include base 10 block manipulatives; a block construction toybox; a logic construction toybox; an area workshop; and MathCats balance. See, in particular, Nummòlt's openended obbl & math toys: adding
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 The Official Scoring Site of the International Mathematical Olympiad 2001  Wolfram Research
The IMO 2001 competition, for students under the age of 20 who have had no postsecondaryschool education, was held July 114, 2001, in Washington, DC, USA. Each country represented is allowed up to six participants. This site records scores and supplies
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 Off The Hypotenuse  Glenn Kenyon
Kenyon started this blog in pursuit of "a good discussion of resources, ideas, and innovative ideas for teachers of Algebra." Humorous videos, comic strips, and posts, which date back to March of 2007, have included "Math Lessons learned from Karate,"
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 Ohio Proficiency and Graduation Practice Tests  Murtaza Ozdemir, Horizon Science Academy Online
Practice math questions culled from the last four Ohio sixth and ninthgrade proficiency tests or the Ohio graduation test. Users receive a detailed report of their score and a list of missed or skipped questions at the end of the test.
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 Old and New Arithmetic  Ivars Peterson (MathLand)
"Three merchants have invested their money in a partnership..." This problem appears in a mathematics textbook known as the Treviso Arithmetic. The original book, written in a Venetian dialect, had no formal title, and its author is unknown. Treviso is
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 Olimpíada Brasileira de Matemática  Sociedade Brasileira de Matemática (SBM)
The Olimpíada Brasileira de Matemática (OBM) is a competition open to all students enrolled in Brazil's fundamental or middle studies. Browse or download archived exam problems and solutions dating back to 1997. Read news about olympiads, or the journal
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 Olimpíadas Portuguesas de Matemática  Soc. Portuguesa de Matemática (SPM)
The Portuguese mathematical Olympiads: history; archive of problems; past winners; rules; the Portuguese team; links to relevant Web sites; and more.
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 Olimpiada Matemática Española  C. SánchezRubio
Convocatoria XXXV Olimpiada (Curso 1998/99); Comisión de la Olimpiada Matemática Española; Información para alumnos y profesores; Problemas de las últimas Olimpiadas (Fase nacional); Material para preparación;
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 Olimpiada Mexicana de Matemáticas  Luis Miguel García Velázquez
Mexican Math Olympiad Official Site. Mathematical Contest with problems,
tests, and other material. In Spanish. Información General de la Olimpiada. Problemas, exámenes y material de estudios. Contactos, noticias y mucho más. Also
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 Oliver Knill
Research, teaching, and media by this preceptor in Harvard's math department. Knill began in dynamical systems, tackling first ergodic and spectral theoretical questions, then probability theory and elementary number theory. This led to his "passion for
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 On Beyond Newton: from Simple Rules to Stability, Fluctuation, and Chaos (Serendip: Complex Systems)  Bryn Mawr College
An interactive exhibit on homeostasis/autonomy/chaos centered around population dynamics. The phenomenon of rules giving rise to not only order but also disorder, and, beyond that, to previously unknown forms of order, is the terrain currently being explored
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 Once in a Millennium (Math Chat)  Frank Morgan, MAA Online
Challenge: The year 2000 can be represented as the sum of consecutive integers:
2000 = 398 + 399 + 400 + 401 + 402. The year 2001 can be represented as the sum of consecutive integers: 2001 = 1000 + 1001. In fact, every year in the millennium from 2000
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 OnePage Proof of Fermat: Critique (Math Chat)  Frank Morgan, MAA Online
Critique the following short proof of Fermat's Last Theorem sent in by
reader Rob Connelly. (In perhaps the biggest mathematics news of the century, Andrew Wiles recently came up with a very long and complicated proof of this 350year old problem.) Answer:
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 One Trip to the Attic? (Math Chat)  Frank Morgan, MAA Online
In the lobby of a hotel there are three on/off switches. One is attached to a light bulb on the third floor; the other two are attached to nothing at all. You may work the three switches as often as you please. How many times do you need to visit the
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 On Four 4s and Speed Limits (Math Chat)  Frank Morgan; Christian Science Monitor
Can you get past 30 in forming numbers 0, 1, 2, 3, ... from four 4s and the standard mathematical operations +,  , x, /, decimal point, square root, powers, and factorial(!)?
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 OnLine Encyclopedia of Integer Sequences  The OEIS Foundation Inc.
Before publishing that new sequence you have just found, you might want to check here to see if it's already been discovered. Directions for how to look up a sequence in the table, abbreviations used, sending in a new sequence; how to look up a reference
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