 BrainBashers  Kevin Stone
Five math or logic challenges on a page, each with clickable hints and solutions. For games, visit http://www.brainbashersgames.com/.
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 Brain Boosters  Discovery Education
An archive of challenging puzzles, organized under: Categorization, Lateral Thinking, Logic, Number and Math Play, Reasoning, Spatial Awareness, Word and Letter Play.
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 Brain Food  Puzzles For the Brain To Gnaw On  Samuel Stoddard
Hundreds of online (CGI) puzzles, including logic puzzles, word problems, number puzzles, lateral thinking puzzles, scrambled equations, cryptograms, loginumber puzzles, discrete reasoning puzzles, mathematical reasoning puzzles, knight's dilemma, magic
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 Brainfreeze Puzzles  Riley, Philip; and Taalman, Laura
Free example puzzles and solving tips for colorful, handdesigned Sudoku variation puzzles with additional rules that challenge you to rethink your old Sudoku strategies and devise new ones. From the authors of the book, Color Sudoku.
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 Brainwave  Wognum Art
Ten visual puzzles, to test your visual and reasoning skills. Most have to do with symmetry recognition. There is a "top 5% brain" award to those who earn ten "smart bulbs."
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 Breaking Chocolate Bars  Cut the Knot!, Alexander Bogomolny
The chocolate bar puzzle has three parameters: two side lengths (m and n) and actual selection of lines along which to break the bar and its parts... An interactive column for MAA Online that uses a Java applet to simulate a puzzle or mathematical problem,
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 Bret Victor
From the creator of Kill Math, Victor's "umbrella project for techniques that enable people to model and solve meaningful problems of quantity using concrete representations and intuitionguided exploration" in pursuit of a "widelyusable, insightgenerating
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 The Bridges of Königsberg  Isaac Reed
This problem inspired the great Swiss mathematician Leonard Euler to create graph theory, which led to the development of topology.
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 The Bridges of Königsberg  Jim Loy
A brief introduction to Euler's Bridges of Königsberg problem, graph theory, and simple related puzzles.
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 Brightest Moon for Thousands of Millennia? (Math Chat)  Frank Morgan, MAA Online
Answer to the challenge: Was there any validity to the claim that the full moon of December 22, 1999 was the brightest that we shall see for millions of years? (Factors that coincided.) New challenge: Eric Brahinsky saw in an article on "New molecule
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 Brilliant
Weekly Olympiadstyle challenges that offer "rigorous, competitive, whimsical, and edifying" problem sets in math and physics. Register to explore the Brilliant Techniques Trainer's practice exercises; answer correctly to earn points redeemable for lanyards,
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 A Broken Calculator  Cut the Knot!, Alexander Bogomolny
Thoughts on the controversial question of using calculators in the classroom, and the author's belief that even a broken calculator may have its uses: the elementary mathematics curriculum may emphasize any or all of the paperandpencil, mental, or technologybased
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 Buffon's Needle  Paul Kunkel
An investigation of the problem: Consider a plane, ruled with equidistant parallel lines, where the distance between the lines is D. A needle of length L is tossed onto the plane. What is the probability that the needle intersects one or more lines?
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 Building Blocks  Doug Clements and Julie Sarama, University at Buffalo, State University of New York
Supplementary and enrichment math materials for young children. Project writings include "Mathematics in the Preschool"; "'Concrete' Manipulatives, Concrete Ideas"; "Mathematics for Young Children"; "Technology and School Change: New Lamps for Old?";
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 Burning 1Hour Fuses in 45 Minutes (Math Chat)  Frank Morgan, MAA Online
You have two onehour fuses: lighting one end of a fuse will cause it to burn down to the other end in exactly one hour's time. You know nothing else about the fuses; in particular you don't know how long any segment of a fuse will burn, only that an
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 The Burr Puzzles Site  IBM
A Burr Puzzle consists of at least three rods intersecting each other at right angles. The most wellknown type is the six piece burr where three sets of two rods intersect each other. This site lets you explore six piece burrs by selecting from a list
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 Byzantine Basketball  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
A problem (with solution) sent by Prof. W. McWorter's: Byzantine Basketball is like regular basketball except that foul shots are worth a points instead of two points and field shots are worth b points instead of three points. Moreover, in Byzantine Basketball
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 C26: Geometry  Scott Thatcher; Dept. of Mathematics, Northwestern Univ., Evanston, IL
Syllabus for a Geometry course, with some solutions to problems in PDF format; Maple worksheets (version 4) for multivariable calculus.
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 Calculator City  1728 Software Systems
Online calculators for solving equations in 2, 3, or 4 unknowns, the Pythagorean theorem, sphere and cylinder area and volume, vector addition, resistors in parallel, chemistry gas laws, compound interest, and loan payments. Games and puzzles include
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 Calculatorium  Nenad Mitrovic
JavaScript calculators for determining area, perimeter, surface area, volume, trigonometry, algebra, statistics, finance, conversions, health, and more. See also Calculatorium's timed, autoscoring tests and typeset formulas.
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 Calcul à Plusieurs Variables  Pierre Joyal, Armel Mercier
Site in French. An abundant documentation on several variable calculus, including numerous Flash and Java animations.
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 CalculusABC.com  Chris Watson
A site for calculus teachers to share questions they've written and discuss
issues relating to the field. Sort multiple choice questions according to calculator use and representation type (verbal, numerical, analytical, or graphical). With web forums
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 Calculus: an Overview  Paul Pollack
Written by a 16yearold, this siteinprogress contains brief summaries of topics for the advanced high school student. Available pages include: Functions: a review; Limits: what they mean and how to find them; Integration practice problems; Taylor and
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 Calculus in Motion  Audrey Weeks
Geometer's Sketchpad animations of mathematical concepts from middle school through high school. Three products are offered: Calculus in Motion (161 animations Including animations of 20091997 AP Exam AB & BC Free Response Questions); Algebra in Motion
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 Calculus&Mathematica  University of Illinois at UrbanaChampaign, Ohio State University
A computerbased course about calculus, differential equations, and matrix theory, which the instructor can use as soon as the computers are unloaded at the classroom door. Includes a complete electronic text combined with a set of problems for the students
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 Calculus on the Web (COW)  Mendoza, Reich; Department of Mathematics, Temple University
A collection of autoscoring calculus modules organized into books, chapters, and sections, with help and hints for the problems. Modules with asterisks (including chain rule, Taylor polynomials, Riemann sums, and arc length) allow you to change values
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 The Calculus Page Problems List  D. A. Kouba, U.C. Davis Department of Mathematics
Problems, with detailed solutions, from beginning differential calculus (limit of a function, continuity of a function, "squeeze principle," chain rule, product rule, quotient rule, differentiation of trigonometric functions, and more); and beginning
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 A Calculus Review  Linda Valdes; San Jose State University, San Jose, CA
An interactive set of eight 12question quizzes on limits, differentiation, and
integration, with hints and reviews of technique. Requires Netscape 4.5 or later.
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 Calculus (S.O.S. Mathematics)  Dept. of Mathematical Sciences, Univ. of Texas at El Paso
An online course: learning units presented in worksheet format review the most important results, techniques and formulas in college and precollege calculus. Logarithms and Exponential; Sequences; Series; Techniques of Integration; Local Behavior of
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 CalMaeth: Computer Aided Assessment and Learning of Mathematical Methods  Mathematics Dept., Univ. of Western Australia
A collegelevel interactive aided teaching and learning system that poses math questions on various topics and then evaluates the student's answer. It is designed for UWA students, but guest login is enabled. A set of demonstration questions will show
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 C.A.L.M. (Computer Assisted Learning Method)  Critical Thinking Inc.
An educational site to help high school students learn plane geometry, featuring algorithmic generation of questions providing individualized questions for each student, immediate feedback regarding the student's response, and tracking routines allowing
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 Camel and Bananas  Math Forum, a Classic Problem from the Ask Dr. Math FAQ
What's the maximum number of bananas the camel can transport across the desert?
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 Card Colm  Colm Mulcahy
This blog "explores mathematical card principles and effects for fun." Inspired by Martin Gardner and his seminal Mathematics, Magic and Mystery, Mulcahy has posted since August, 2011: "A Call For A New Shuffle Principle (Need Rot Sextet?)," "Splitting
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 Carl Eberhart
Class information and/ or Maple worksheets for courses including multivariable calculus, linear algebra, linear programming, differential equations, numerical methods, and topics for mathematics teachers, as well as Maple and C++ programs for a course
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 Carré d'As  Carré d'As
Mathématiques amusantes pour vous détendre: questions et solutions, challenges, la question des champions (qui sera remplacée quand 20 internautes auront réussi à trouver la solution avec une démonstration correcte dès le premier essai), et 229 questions
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 CARROLLIA  Mensa España  CarrollSIG
El órgano de comunicación del CARROLLSIG de Mensa España, que se dedica a las matemáticas recreativas, la lingüística, la literatura experimental, la lógica, la ciencia, y todo aquello que hubiera gustado
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 CATS: Combinatorial Algorithms Test Sets  ACM Journal of Experimental Algorithmics (JEA)
Mission: to facilitate experimental research by standardizing common benchmarks, providing a mechanism for their evolution, making them easily accessible and usable, and identifying significant open questions in the design of good test sets and the assessment
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 Cattle of the Sun  Ivars Peterson (MathTrek)
The story goes that Archimedes of Syracuse (287212 B.C.) was annoyed with Apollonius of Perga (262190 B.C.), who had criticized Archimedes' work on the multiplication of large numbers. For revenge, Archimedes devised a fiendish computational problem
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 CAUSEweb  Dennis K. Pearl, Director
The Consortium for the Advancement of Undergraduate Statistics Education (CAUSE) collects, reviews, develops, and disseminates resources for members of the undergraduate statistics education community. Resources include lesson modules for lecturers; computer
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 cavmaths  Stephen Cavadino
Blog by a maths teacher and KS5 coordinator. Posts, which date back to July, 2012, often incorporate social media and snapshots of scratch work: "Christmaths Projects," "Engaging with Written Feedback," "Consistency, Humour, Well planned Lessons and
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 Census Challenges (Math Chat)  Frank Morgan; Christian Science Monitor
Gordon Squire notes that planners for the 2000 U.S. Census wonder what to do about missing certain groups of people such as many homeless in New York. Suggestions include statistical random sampling. What approach would you suggest?
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 Centre for Education in Mathematics and Computing (CEMC)  Faculty of Mathematics, University of Waterloo, Canada
Home of the Canadian Mathematics Competitions (CMC); the Canadian Computing Competition; and contests for middle and high school students. Download PDFs of contest problems dating back to 1997. Register, obtain results from the competitions, participate
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 Centre for Innovation in Mathematics Teaching  University of Plymouth
A focus for research and curriculum development in mathematics teaching and learning with the unifying aim of enhancing mathematical progress in schools and colleges. The site includes: The Mathematics Enhancement Programme; Resources: worksheets in HTML
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 The Cereal Box Problem: A Lesson in Expected Value (MSTE)  George Reese; University of Illinois at UrbanaChampaign (UIUC)
Collect all six! How many cereal boxes would you expect to have to buy to get all the prizes? This lesson examines this expected value question and includes an online simulation.
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 Challenges: Mathematics and Statistics  InnoCentive, Inc.
"Seekers" submit challenges to InnoCentive's online marketplace for innovation, where scientists, engineers, professionals and entrepreneurs collaborate to solve them. The most innovative solutions receive financial awards ranging up to US$1,000,000.
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 Challenges  RSA Security
Read about three cryptographic challenges: RSA Factoring Challenge, SecretKey Challenge, and DES Challenge III. For the solution of these cryptographic challenges, RSA offers cash prizes as "... modest rewards for some of the hard work that goes into
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 Chance Encounters at ICME9  Cut the Knot!, Alexander Bogomolny
From the International International Congress on Mathematics Education held in Tokyo in August, 2000, impressions that came from personal, often unplanned, meetings with such mathematicians as N. P. Dolbilin (who outlined the history and the current state
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 The Chaos Game  Robert L. Devaney; Dept. of Mathematics, Boston University
One of the most interesting fractals arises from what Michael Barnsley has dubbed "The Chaos Game," which is played as follows. First pick three points at the vertices of a triangle. Color one of the vertices red, the second blue, and the third green.
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 Chaotic Dynamical Systems (Serendip)  Victor J. Donnay; Bryn Mawr College
In dynamical systems, an object moves according to a rule. Depending on the rule motion, the object may move in a regular fashion or in a chaotic fashion. This project by Prof. Donnay, his students, and colleagues illustrates the ideas of chaos theory
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 Chase Four Sketches  Bill Finzer, Key Curriculum Press
A sketch and a script to answer the question: if there are four ants in the plane and each crawls continuously toward the next ant, what do their paths look like?
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