 Conundrum Corner  UselessKnowledge.com
Math puzzles to solve, get the answers to, or send to friends. Also, Visual puzzles, Thinking puzzles, and other conundra.
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 Converting Inches to Miles  NASA Lewis Learning Technologies Project
The scale on a road map is 1 inch = 250 miles, how many inches would represent 1250 miles? A detailed answer is provided. From NASA's 9th Grade Math Proficiency Test.
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 Converting Tons to Pounds  NASA Lewis Learning Technologies Project
A loaded moving van weighs 5 tons. How many pounds would 10 loaded moving vans weigh? A detailed answer is provided. From NASA's 9th Grade Math Proficiency Test.
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 coolmath.com: Cool Math  Karen
A searchable "amusement park of mathematics" for exploring math: functions, tessellations, polyhedra, limits, logs, fractals (with galleries), puzzles and problems, fun with numbers, how to succeed in math, careers in math. Also Cool Links for Math for
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 Cool Math Dudes  ThinkQuest 1996
Problems to explore, with solutions: Investment Inquiry; Circle Selections; The Beginning of Breanna; Matrices Mayhem; Breanna Returns.... With a Watch; Roots of Algebra; Breanna's Chess Companions; Squares of All Shapes and Sizes (well, not of all shapes);
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 CopyCat  Jim Morey
A Java game that revolves around replicating a picture created by several patterned faces of a solid object (like a cube), challenging the mind to understand complex geometrical structures and symmetry. To do well at the game, the player must first become
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 Count Down to Fall  Fran Hawk, Sherry Neidigh (ill.)
Seasonal counting fun with this picture book. This title also includes the Sylvan Dell “For Creative Minds” section with lessons like “Plant Parts,” “The Shape of It All,” and “Match the Leaves.” Check out all these activities at the book homepage, along
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 The Counterfeit Coin  Ivars Peterson (MathTrek)
The classic puzzle of the counterfeit coin has long served as a stiff test of one's reasoning power and ingenuity. In its standard form, the problem concerns 12 coins identical in size, shape, and appearance. One coin, however, is counterfeit, having
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 The Counting Game  Chris Malumphy
A game for children starting to count, showing a number of objects and asking you to click on the correct number button. A thermometer graphic tells you when you have correctly answered ten questions.
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 Counting Hamilton Cycles in Product Graphs  Frans Faase
Exploration of Hamilton paths through a program which draws a snake that starts at one place in a box, and then extends itself until it cannot go further, after which it shrinks again, to seek another path. The author coded these snake programs in Fortran,
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 Count Madness Number Puzzles  James E. Garner
Cards with questions covering a wide range of subjects, each of which can be answered with a counting number. Answers are upsidedown on the card. Examples and ordering information provided on site. Teacher's copy available.
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 Count Mathula  Michelle Anderson
Worksheets for Anderson's Algebra III and Trigonometry classes, available as MS Word downloads, editable using MathType, and also as PDFs: functions, complex numbers, trigonometry. Resources include premade graph paper in PDF format to download.
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 Count On  Department for Education and Employment, UK
Activities and resources  some simple and some fancy  for parents, teachers, and students. Resources offers, among other things, guides: to mathematical misconceptions; for parents helping with homework; for promoters of math fairs; and for providers
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 CourseServer  Jud Cornish; Fairbanks Country Day School, San Diego, CA
A Webhosted math problem generator that allows you to select from thousands of different problem types and automatically generate problemandanswer worksheets in your browser that can be printed out. Choose from a list of courses from Grade 1 (beginning
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 The Cow in the Classroom  Ivars Peterson (MathLand)
Math Curse by Jon Scieszka and Lane Smith spoofs the types of word problems that educators and textbook writers invent to dress up arithmetic exercises and, supposedly, to demonstrate the relevance of math to everyday life. Canadian economist and humorist
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 Cracking a Medieval Code  Ivars Peterson (MathTrek)
The first printed book on cryptology was written by Johannes Trithemius (14621516), an abbot in Spanheim, Germany, who was one of the leading intellectuals of his day. Bearing the title Polygraphiae libri sex ("Six Books of Polygraphy"), it was published
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 Cracking the Myth of Ball Control  Ivars Peterson (MathLand)
Ball control has become common practice in a number of sports. In basketball, for example, coaches often urge their teams to slow down a game at certain times or to control its tempo. In professional football, "time of possession" has become a statistic
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 Creative Java Puzzles  J. L. Read, Enchanted Mind
Games "good for exercising both sides of the brain." Knight's Tour: pass all the squares of the board with the knight, making only legal moves. Peg Solitaire: Remove all the pegs in the least amount of time, finishing with only one peg in the target hole.
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 Crossnumber puzzle (figure logic)  Alfredo Baratta
Cross figure puzzles to print or play online. Also known as figure logic puzzles, cross figure puzzles resemble crosswords in structure, but with entries consisting of numbers rather than words, and clues based on math questions, e.g., "1 Across: The
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 Cross Number Puzzles  Rainer Typke
Cross number puzzles to solve online; log in to create your own. Also known as crossfigure, figure logic, or numberlock puzzles, cross number puzzles require numbers instead of words to complete a crosswordlike grid.
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 Cryptarithms Online  Jorge Soares
Mathematical puzzles in which the digits are replaced by letters of the alphabet or other symbols. Brainteasers by the author; cryptarithms from the journal Sphinx; a primer; books on cryptarithms, and links to relevant sites on the Web.
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 Cryptoclub  Vera Pless, Janet Beissinger
This website includes tools to encrypt and decrypt messages, an
animated treasure hunt, a classroom message board to send and
receive encrypted messages, and a place to explore mathematics
topics related to cryptography, such as prime numbers and
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 The Crypto Drop Box of the American Cryptogram Association  Jerry Metzger
The American Cryptogram Association (ACA) is a nonprofit volunteer organization devoted to disseminating cryptographic knowledge. Members make up and solve their own creations strictly for the fun of it. Every two months, the ACA journal, The Cryptogram,
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 Cryptography  Corey Reed
An introduction to cryptography, in particular affine enciphering applied to the alphabet, focusing on the use of linear algebra. Includes a primer on bases and modulus algebra and extensions for deciphering an affine enciphered message, using keys to
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 CTAP Middle School Math Project  CTAP Region IV
A database of online technology resources supporting California middle school math content standards for grades 6, 7, and algebra. Designed for use in classroom instruction or as homework helpers for students, the matrices resources align to state standards
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 C.T.J. Dodson  Christopher Dodson
Dodson provides notes and Maple or Mathematica packages for many different mathematics courses, including algebra and precalculus, calculus, differential equations, using computers for mathematics and statistics, and an introductory course on curves,
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 The CTK Exchange  Interactive Math Miscellany and Puzzles, Alexander Bogomolny
A page devoted to questions and answers concerning Bogomolny's pages and math in general. Postings are approved by Bogomolny, and usually answered by him, although they may be answered by the general public as well. Posting topics vary all the way from
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 Curious and Useful Math  Clay Ford
Tricks and rules for quickly calculating certain types of math problems, many from the 1888 book The Carpenter's and Joiner's Pocket Companion. Multiplication Tricks; Division Tricks; Squaring Tricks; Can it Divide...?; Age Math; Bible Numbers; Box Tricks;
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 The Curious Creative: Maths  Tom Barrett
Blog by a former teacher and ICT Subject Leader. Barrett's math posts, which date to back to July, 2006, have included "Addressing the Balance: Multiflyer Times Tables Challenge," "Using Nintendo Wii Sports for Addition and Subtraction," "My Maths Lesson
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 The Cutting Sticks Problem  Frans Faase
A classic math puzzle: You are given k sticks with integer length of which the total length of sums up to n(n+1)/2. None of the sticks is shorter than n. Can you always cut them into sticks with length 1, 2, up to n, no matter the number of the sticks
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 CYBERCHASE Online  Educational Broadcasting Corporation (PBS.org)
Companion site to CYBERCHASE, PBS's animated math adventure series, intended to foster math literacy and problemsolving skills for kids ages 811. Play interactive games or practice with tools such as the talking calculator, crack challenging puzzles,
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 The Cyclotomic Fields Virtual Study Group
A group of people studying L. Washington's book Introduction to cyclotomic fields. Download solutions to the book's problems in DVI format, or read the list of errata.
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 CyMath
Stepbystep typeset results in differential calculus, integral calculus, algebra, and trigonometry. Just key in your expression or equation — or modify one of CyMath's examples — then select from among eight actions in the pulldown menu:
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 Dad's Worksheets  Dad
Dad's Worksheets is a site with strategies and free printable practice worksheets (including answer keys) for elementary math operations.
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 Daily Desmos  Anderson, Dan; Fenton, Michael; and Lanier, Justin
A daily challenge to reproduce a given graph using Desmos or some other graphing calculator. Teachers Anderson (NY), Fenton (CA), and Lanier (NY) rate the plots by difficulty. Also available from http://dailydesmos.blogspot.co.uk/.
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 DA Information  David Hoffman
An introductory course in decision analysis, with lecture notes and instructions for projects.
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 Data Games  KCP Technologies
As students play Data Games, they generate data that they must analyze to win the games. Supporting materials include a student worksheet; teacher guidelines that correlate the activity to the Common Core State Standards for Mathematics (CCSSM); and videos
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 DAU Math Refresher Tutorial  George Mason University
An interactive tutorial that uses a subway map as a metaphor for moving through the lessons, giving a comprehensive view of basic mathematics, covering arithmetic, fractions, exponents, logarithms, quadratic equations, series, functions, limits, domains
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 David Eppstein's Teaching  David Eppstein
Archives of Information and Computer Science courses in computational statistics, computability, design and analysis of algorithms, computational geometry, game programming (Java versions of mancala, othello, and fanorona), graduate data structures, computational
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 David Goodman's Math Links  David Goodman, editor
Link listings for a variety of topics, organized by those topics.
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 David Sumner's Home Page  David Sumner
Study guides, exams, quizzes, problem sets, exam review materials, utilities, programs and simulations, syllabi, and other materials for courses such as calculus, sequences and series, graph theory, number theory and cryptography, and probability. The
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 Davitily Math Problem Generator  Nguyen, Ly; and Pardue, David
Create worksheets and tests, including options for multiple choice, printable versions, and answer keys. Click to insert preworded questions in basic math, algebra, and geometry, the parameters of which vary randomly. Requires JavaScript. Also available
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 Dear Marilyn, About Leap Years (Math Chat)  Frank Morgan, MAA Online
Your explanation [in Parade Magazine] of September 13, 1998 that we may need to skip a leap year EVERY FEW THOUSAND YEARS because the tropical year (about 365.2422 days) is a bit shorter than the average calendar year (365.2425 days) neglects CHANGES
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 Deberes matemáticas: Ejercicios y problemas de matemáticas resueltos paso a paso.  FORTEC, Formación y Tecnología S.L.
Herramientas didácticas específicas para la enseñanza y el aprendizaje de las matemáticas de la E.S.O. Ejercicios, problemas, exámenes, temarios, todos resueltos y explicados paso a paso. Por suscripción.
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 Decimal Places on a Number Line  NASA Lewis Learning Technologies Project
Decimal places: On a number line, which of the following numbers would be the farthest to the right? 0.001, 0.0015, 0.00099, 0.0005. A detailed answer is provided. From NASA's 9th Grade Math Proficiency Test.
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 Deep in the Jungles  Ivars Peterson (MathTrek)
Humans are predisposed to seeing order and meaning in a world that too often presents random choices and chaotic evidence. Random events sometimes get linked into a meaningful, though ultimately bogus, scenario... At the same time, the mathematics of
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 The Definitive Four Fours Answer Key  David A. Wheeler
From 0 up to 40,000, whole number mathematical expressions that use only common mathematical symbols and exactly four 4s. Wheeler offers his solutions in three different formats: an abbreviated list of answers; a text file of results, mathematical expressions,
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 Delphi For Fun  Gary Darby; Intellitech Systems Inc.
Delphi is based on the Pascal programming language developed in the early 1970s by Niklaus Wirth and named after mathematician Blaise Pascal. This site explores the use of programming as a tool in math problem solving, discussing interesting problems,
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 Delta Blocks  Hop David
A way to model different 3D tessellations and a tool for studying geometry, crystallography, and polyhedra. Delta blocks were inspired by M. C. Escher's print "Flatworms," which he said demonstrates that one can build a house not only with the usual
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 Department of Higher Mathematics, PhysicoTechnical Institute  Moscow State University
In Russian. Information on the department, study materials (textbooks and study aids by the dept. teachers, previous exams, lists of programs and classes and conferences for the current year), and information and download of a mathematical computer program
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