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  All Sites - 521 items found, showing 201 to 250

  1. Fraction Riddle - Joyce , 09/05/2003
    How can 1/2 of 9 be 4? ...more>>

  2. Freezer Roulette - Kev, 07/26/2002
    Two people are trapped in a small freezer that is slowly getting colder and colder... Is it possible for them to escape? If so, how? What’s the maximum number of minutes required to escape given ANY initial combination of button states? ...more>>

  3. Friday the 13ths in a Year - Cole, 08/10/1999
    How can I figure out the maximum number of Friday the 13ths there are in one year? ...more>>

  4. Frogs Changing Sides - Jean, 09/04/2002
    What is the least number of jumps needed for all the frogs to trade sides? ...more>>

  5. Fun Addition - Horick, 8/21/1995
    Given the numbers 1 through 9, using each number only once, how many problems can be formed when adding two three-digit numbers? Is the sum of the digits in the sum always 18? ...more>>

  6. Fun Brain Twister - AQ, 8/22/1996
    Use six 7's to write an expression that has a value of 110. ...more>>

  7. A Game in Three Rounds - Razelene, 04/19/1999
    After three rounds each of the girls has 8 chips. How many chips did they have at the start? ...more>>

  8. Game of 24 - Kurtz, 7/15/1996
    A student takes four numbers and combines them by addition, subtraction, multiplication, division, or a combination thereof to produce an answer of 24. ...more>>

  9. The Game of 24 - Rosenbaum/Mahon, 3/14/1995
    Using addition, subtraction, multiplication, and division, can you use 7,7,3,3 to make 24? ...more>>

  10. A Geometry and a Logic Problem - Marsville, 3/11/1995
    Problem 1: A cylindrical hole six inches long is drilled straight through the center of a solid sphere. What is the volume remaining in the sphere? Problem 2: The classical stay-switch problem. ...more>>

  11. Geometry Puzzles - Creswell, 12/18/1995
    A student asks Dr. Math for help in finding the correct combinations of numbers to solve two puzzles. ...more>>

  12. Getting All the Utilities to Each House - Borstein, 5/17/1995
    There are three houses and three different utilities. Can you connect each utility to each home WITHOUT crossing any lines? ...more>>

  13. The Gift of the Magi - Cassie, 09/08/2002
    What mathematical error can be found in the first paragraph of O. Henry's 'The Gift of the Magi'? ...more>>

  14. Girls and Coins - Shana, 01/29/2001
    Five girls stopped for a soda on the way home from school. The girls were amazed to find that each of them had exactly six coins... ...more>>

  15. Giving Myself a Challenge - Stephanie, 09/20/2014
    A student wonders if doing puzzles from math competitions would help her as she prepares for her advanced coursework. Doctor Ian suggests many ways to exercise lateral thinking skills, mathematical insight, and creativity in problem-solving no matter ...more>>

  16. Grains of Wheat - Khalafalla, 07/14/1999
    The person who invented the game of chess was said to have been offered any payment he wanted... How much wheat did he receive? ...more>>

  17. Grandfather Clock and 7-Second Chime - Cindy, 06/06/2002
    If it takes a grandfather clock 7 seconds to chime 7 o'clock, how long will it take the same clock to chime 10 o'clock? ...more>>

  18. Grid Game - Chad, 07/20/2001
    This game for two players is played on a rectangular grid with a fixed number of rows and columns. Play begins in the bottom left-hand square... ...more>>

  19. Guess and Check - Johnathan , 06/17/2002
    The sum of two numbers is 15. The difference is 3. What is the product? ...more>>

  20. Guess and Check - How Many Coins? - Christine , 10/03/2002
    Jeremy has seven fewer coins than Hanna. If together they have 83 coins, how many coins does Hanna have? ...more>>

  21. Guessing a Mystery Number - Akash, 05/23/2007
    One person thinks of a natural number and the other person has to try to guess it by asking questions. The one who knows the number will lie once at some point, but otherwise be truthful in answering the questions. What's the best algorithm for finding ...more>>

  22. Half of Five is Four? - Don, 11/04/2004
    What's the only number system where half of five is four? ...more>>

  23. Handshake Problem Variant - Bixler, 07/08/1999
    Five couples go to a party and start shaking hands. One of the men shouts, "Stop! How many hands did you shake?" Every person gives a different answer... ...more>>

  24. The Haybaler Problem: Reflections and Refinements - Anonymous , 10/05/2002
    Given pairwise weights, a student and Doctor Greenie reflect on how to deduce individual ones before a PhD follows up with several simplifying insights of his own. ...more>>

  25. Heads and Legs - Joseph, 07/25/2001
    Joe counts 48 heads and 134 legs among the chickens and dogs on his farm. How many dogs and how many chickens does he have? ...more>>

  26. Headscratch Letter Puzzle - Ting, 01/25/2002
    Use the numbers 0 to 9 for each letter once: G*B=HA, D*E=E, I*C=C, H* A=DE, F*J=GJ. ...more>>

  27. A Hen and a Half - Chase, 09/23/1998
    If a hen and a half lays an egg and a half in a day and a half, how many eggs will five hens lay in 6 days? ...more>>

  28. Hidden Faces in a Set of Cubes - Roden, 10/04/2000
    Can you give us a hint for a formula that will tell you the number of hidden faces in an arrangement of a cubes if you know the number of visible faces? ...more>>

  29. Hit-and-Run Prime Number Problem - Charlie, 12/10/2002
    Did you get his license number? ...more>>

  30. Hole in a Sphere - Klein, 12/30/1996
    When you bore a 6 inch cylindrical hole through the center of a sphere, what is the volume of the remaining solid? ...more>>

  31. How Does the Crystal Ball Know What Number I Chose? - Cheryl, 01/05/2010
    Doctor Ian reveals how a mind-reading crystal ball "knows" the number you've chosen: represent any two-digit number 'ab' as 10*a + b.... ...more>>

  32. How Does the Fido Puzzle Work? - Karen, 05/12/2004
    Can you give me the mathematical explanation of how the Fido puzzle works? You can find the puzzle at http://digicc.com/fido/. ...more>>

  33. How Heavy is the Brick? - Malligan, 11/15/1997
    If a brick weighs a kilogram plus half a brick, how heavy is the brick? ...more>>

  34. How Many Friday the 13ths - Smith, 9/12/1996
    Is there a way to figure how many Friday the 13ths can occur in a given year? ...more>>

  35. How Many Games Were Tied? - Laura, 06/07/1999
    How many games are tied if each team receives 3 points for a win, 1 point for a tie, and no points for a loss, and after 4 rounds the accumulated points are: Lions 22, Tigers 19, Mounties 14, Royals 12? ...more>>

  36. How Many Handshakes? - Kathy, 01/29/2001
    There are 40 people in a room. They shake each other's hands once and only once. How many handshakes are there altogether? ...more>>

  37. How Many Hidden Faces? - Amy, 07/07/2002
    When you place a number of cubes in a row on a surface, how many of the faces can't be seen from any position? Is there a formula for this? ...more>>

  38. How Many Pencils? - Thomas, 09/05/2001
    How many pencils does Al have if all of them are blue except 2, all of them are yellow except 2, and all of them are red except 2? ...more>>

  39. How Many People Went on the Cruise? - Jessica, 12/03/2001
    At the end of a special cruise, the employees could not remember the total number of people who were on board. However, they had the following data from the passenger list: 520 European females... ...more>>

  40. How Much Money? - Jessica, 08/16/2001
    A man has 3 daughters, 4 sons, and a sum of money. If he divides the money equally among his daughters $2 will be left over... ...more>>

  41. How Old is Korinth? - Phillips, 09/09/1997
    Korinth is twice as old as Marin was when Korinth was as old as Marin is now. Marin is 18. ...more>>

  42. How to Create a 4 x 4 Magic Square - Bernard, 01/28/2004
    Is there a general technique for creating a 4 x 4 magic square so that the rows, columns, diagonals, four center squares and four outside corner squares each add up to a desired number? ...more>>

  43. How to Make a Square with Three Lines - Gary, 06/19/2001
    My teacher says it is possible to make a square with three lines, but I don't know how to do it. Can you help me? ...more>>

  44. The Hundred Fowls - Yana, 09/29/2001
    If a rooster is worth five coins, a hen three coins, and three chickens together are worth one coin, how many roosters, hens, and chickens totaling 100 can be bought for 100 coins? ...more>>

  45. I am 5 digits long... - Ceste/Larioni, 12/16/1994
    ... I am divisible by 3 and 9, but not 6; my digits add up to 27... ...more>>

  46. If 1/x+x=5, what does 1/x^2+x^2 equal? - Shawn, 08/16/2002
    A complex and an easy solution to the problem. ...more>>

  47. Impossible Word - Babler, 04/14/2001
    What word comes out to 575,151 when you multiply together the values of its letters? ...more>>

  48. Indefinite Series, Perfect Squares - Connie, 01/01/1998
    Across the first row of an 11-column table are the numbers 1991, 1992, 1993, .... 2000, 2001. ...more>>

  49. Jack is Older than Jill - Danielle, 11/16/2001
    If you reverse the digits in Jack's age, you get Jill's age. The sum of their ages equals 11 times the difference between them. Jack is older than Jill. What are their ages? ...more>>

  50. Jack & Jill Mind Teaser - Staley, 8/29/1995
    If Jack had a 5 gal. bucket and Jill had 3 gal. bucket, and they each carried an equal amount to fill an 8 gal. bucket, how was this accomplished? ...more>>

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