Here is a site that updates puzzles regulalry:
 mathschallenge.net
  • Irrationality Of E 17/10/2010 01:00

    Prove that e is irrational.

    Problem ID: 377 (17 Oct 2010) / Difficulty: 4 star
  • Rectangle Construction 17/10/2010 01:00

    Find the connection between the constructed length and the original rectangle.

    Problem ID: 376 (17 Oct 2010) / Difficulty: 2 star
  • Inscribed Circle In Isosceles Triangle 16/08/2010 01:00

    Find the radius of the circle inscribed inside the isosceles triangle.

    Problem ID: 375 (16 Aug 2010) / Difficulty: 2 star
  • Multiplying Magic Square 16/08/2010 01:00

    Show how the values 1, 2, 4, 8, 16, 32, 64, 128, and 256 can be placed in a 3x3 square grid so that the product of each row, column, and diagonal gives the same value.

    Problem ID: 374 (16 Aug 2010) / Difficulty: 3 star
  • Polynomial Roots 07/08/2010 01:00

    Prove that the roots of the polynomial, xn + cn-1xn-1 + ... + c2x2 + c1x + c0 = 0, are irrational or integer.

    Problem ID: 373 (07 Aug 2010) / Difficulty: 3 star
  • Hops And Slides But Never Square 07/08/2010 01:00

    Prove that the minimum number of moves to completely reverse the positions of the coloured counters can never be square.

    Problem ID: 372 (07 Aug 2010) / Difficulty: 3 star
  • Irrationality Of Pi 24/12/2009

    Prove that π is irrational.

    Problem ID: 371 (24 Dec 2009) / Difficulty: 4 star
  • Square And Round Plugs 24/12/2009

    Which fits better... a round plug in a square hole or a square plug in a round hole?

    Problem ID: 370 (24 Dec 2009) / Difficulty: 2 star
  • Algebraic Cosine 30/11/2009

    Prove that cos(x) is algebraic if x is a rational multiple of Pi.

    Problem ID: 369 (30 Nov 2009) / Difficulty: 4 star
  • Inscribed Square 30/11/2009

    Find the side length of the square inscribed inside the right angled triangle.

    Problem ID: 368 (30 Nov 2009) / Difficulty: 2 star
  • Infinite Circles 15/11/2009

    What fraction of the large red circle do the infinite set of smaller circles represent?

    Problem ID: 367 (15 Nov 2009) / Difficulty: 4 star
 Scientific American - Math
  • What’s the Deal with Euclid’s Fourth Postulate? 21/04/2014 13:30
    In February, I wrote about Euclid’s parallel postulate, the black sheep of the big, happy family of definitions, postulates, and axioms that make up the foundations of Euclidean geometry.

    -- Read more on ScientificAmerican.com
  • A Month of Math, Magic and Mystery 16/04/2014 16:52
    Haven't got the Math Awareness Month bug yet? Here are three teasers to get you started: 1. What read the same right side up and upside down, and combine mathematics, art, and language?

    -- Read more on ScientificAmerican.com
  • The Secret Spiritual History of Calculus 14/04/2014 13:00
    Integral calculus originated in a 17th-century debate that was as religious as it was scientific

    -- Read more on ScientificAmerican.com
  • 5 Tips for Faster Mental Division (Part 2) 13/04/2014 15:00
    The Math Dude: Quick & Dirty Tips to Make Math Simpler

    -- Read more on ScientificAmerican.com
  • 5 Tips for Faster Mental Division (Part 1) 12/04/2014 15:00
    The Math Dude: Quick & Dirty Tips to Make Math Simpler

    -- Read more on ScientificAmerican.com
  • Measure Yourself by the Standard of the Capybara 11/04/2014 13:30
    We all know a lot of measurements about ourselves. You are some number of feet or meters tall. You weigh some number of pounds, kilograms, or stone.

    -- Read more on ScientificAmerican.com
  • The Slowest Way to Draw a Lute 07/04/2014 13:30
    Last month, I went to a talk by mathematician Annalisa Crannell of Franklin and Marshall College called Math and Art: the good, the bad, and the pretty.

    -- Read more on ScientificAmerican.com
  • How to Calculate with Significant Figures 05/04/2014 15:00
    The Math Dude: Quick & Dirty Tips to Make Math Simpler

    -- Read more on ScientificAmerican.com
  • A Brief History of Infinitesimals: The Idea That Gave Birth to Modern Calculus 04/04/2014 14:00
    Learning to see the infinite in lines, planes and solids changed math forever

    -- Read more on ScientificAmerican.com
  • Magic, Puzzles Delight Math Fans at G4G 01/04/2014 22:15
    From March 20-23, Atlanta attracted hundreds of people with diverse backgrounds who communicated in the lingua franca of Martin Gardner. Perhaps the last true polymath, Gardner has inspired so many...

    -- Read more on ScientificAmerican.com
  • Graham’s Number Is Too Big for Me to Tell You How Big It Is 01/04/2014 13:15
    I was going to write an April Fool’s Day post with the title “Mathematicians Declare Graham’s Number Equal to Infinity.” Graham’s number is really big, but of course,...

    -- Read more on ScientificAmerican.com
  • Unscientific Unamerican, and Other April Fools' Jokes in SA History 01/04/2014 12:30
    The more complex the mind, the greater the need for play. Okay, I ripped that off from Star Trek, episode 15, but I like to think the conceit applies to the Scientific American community of readers,...

    -- Read more on ScientificAmerican.com
  • Chaos Theory Pioneer Nabs Abel Prize 27/03/2014 14:20
    Yakov Sinai has developed fundamental tools for the study of unpredictable phenomena

    -- Read more on ScientificAmerican.com
  • Quantiphobia and the turning of morals into facts 25/03/2014 22:38
    When stats-wiz and political prognosticator Nate Silver’s new venture, FiveThirtyEight, launched last week, it punctuated the rise of “data journalism,” journalism that incorporates...

    -- Read more on ScientificAmerican.com
  • When It Comes to the Baseball Stat Rage, Quantification Doesn't Always Make It Science 25/03/2014 12:45
    To paraphrase Inigo Montoya, this baseball stat—“I do not think it means what you think it means”

    -- Read more on ScientificAmerican.com
  • Mathematical Impressions: The Bicycle Pulling Puzzle 22/03/2014 12:00
     If you pull straight back on the lower pedal of your bicycle, will the bike move forward or backward? This classic puzzle has a surprising twist

    -- Read more on ScientificAmerican.com
  • These Tips Can Drive You up the Wall 19/03/2014 11:45
    Physics students at the University of Leicester in the U.K. worked out the principles for keeping a speeding race car in control on a vertical curved wall. Wayt Gibbs reports  

    -- Read more on ScientificAmerican.com
  • Take Me Out to the Run Expectancy Matrix Analysis 18/03/2014 15:00
    Smith College economics professor Andrew Zimbalist talks about his latest book, The Sabermetric Revolution: Assessing the Growth of Analytics in Baseball (co-authored with Benjamin Baumer), at the...

    -- Read more on ScientificAmerican.com
  • A Different Pi for Pi Day 14/03/2014 11:30
    The symbol is overloaded in math: depending on context and capitalization, could be the constant we all know and love (or hate), a projection, a product, or a function.

    -- Read more on ScientificAmerican.com
  • Mathematical Patterns in Sea Ice Reveal Melt Dynamics 13/03/2014 18:55
    Some people call Ken Golden the "Indiana Jones" of mathematics due to his frequent excursions to remote, harsh parts of the world. Golden, a professor of mathematics at the University of Utah,...

    -- Read more on ScientificAmerican.com
  • The Math Wars, Lewis Carroll Style 04/03/2014 13:30
    In 1879, Charles Dodgson, better known as Lewis Carroll, published an odd little book called Euclid and his Modern Rivals (available for free at the Internet Archive).

    -- Read more on ScientificAmerican.com
  • Equations Are Art inside a Mathematician’s Brain 04/03/2014 13:00
    A brain area associated with emotional reactions to beauty activates when mathematicians view especially pleasing formulas  

    -- Read more on ScientificAmerican.com
  • A Fluid New Path in Grand Math Challenge 27/02/2014 20:00
    A daring speculation offers a potential way forward in one of the great unsolved problems of mathematics: the behavior of the Navier-Stokes equations for fluid flow

    -- Read more on ScientificAmerican.com
  • The Stunning Symbiosis between Math and Knitting [Slide Show] 24/02/2014 21:30


    -- Read more on ScientificAmerican.com
  • The Stunning Symbiosis between Math and Knitting [Slide Show] 24/02/2014 21:00
    A meeting of the minds at the intersection of mathematics and fiber arts yields eye-popping creations

    -- Read more on ScientificAmerican.com