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
  • Art and Science of the Moiré 15/09/2014 21:40
    I’m a bit obsessed with Scientific American covers, but my knowledge of the archive during the years before my time on staff is broad rather than deep.

    -- Read more on ScientificAmerican.com
  • Book Review: <em>What If?</em> 13/09/2014 15:00
    Books and recommendations from Scientific American

    -- Read more on ScientificAmerican.com
  • Scotland Vote Splits Scientists in Nation Where Dolly the Sheep Was Cloned 10/09/2014 20:05
    Research could founder or flourish if Scotland leaves the U.K., depending on whom you ask

    -- Read more on ScientificAmerican.com
  • Diversity in STEM: What It Is and Why It Matters 10/09/2014 18:08
    Innovations resulting from science, technology, engineering and mathematics (STEM) fields have positively touched nearly every aspect of human life.

    -- Read more on ScientificAmerican.com
  • Beauty in Math and Art Activate Same Brain Area 07/09/2014 16:00
    Elegant equations evoke the same activity in mathematicians' brains as gorgeous art or music

    -- Read more on ScientificAmerican.com
  • This Week in World War I: September 5, 1914 05/09/2014 15:00
    Censored: How the Army Eats In this issue, a telling line reads: "The censors have not allowed the press of the world to state whether or not explosives were dropped on the fortifications of...

    -- Read more on ScientificAmerican.com
  • Mathematics, Live: A Conversation with Evelyn Boyd Granville 05/09/2014 13:30
    Evelyn Boyd Granville was one of the first African American women to earn a Ph.D. in mathematics. She recently turned 90, and I wrote a post here to celebrate.

    -- Read more on ScientificAmerican.com
  • How the Survivor Bias Distorts Reality 04/09/2014 13:00
    How the survivor bias distorts reality

    -- Read more on ScientificAmerican.com
  • Hooked on Metrics: Why Learning Can and Should Be Measured 03/09/2014 16:00
    The following is a guest post by Scott Bennett, principal of eSTEM Academy in Reynoldsburg, Ohio When I first started teaching science 10 years ago, no one ever talked about achievement or thought...

    -- Read more on ScientificAmerican.com
  • Ancient Babylonian Number System Had No Zero 31/08/2014 14:00
    As I told my class on Thursday, the theme of the first week of our math history course was "easy algebra is hard in base 60." We started the semester in ancient Mesopotamia, trying to understand...

    -- Read more on ScientificAmerican.com
  • ScienceArt Exhibits Through September and Beyond 30/08/2014 01:06
    The inside scoop on the best science art exhibitions around the country: EXHIBITS: NORTHEAST REGION LIFE: Magnified June – November 2014 Gateway Gallery Between Concourse C and the AeroTrain...

    -- Read more on ScientificAmerican.com
  • Satirists As a Source of Science News 29/08/2014 14:33
    How many times have you read a science-themed article from The Onion or watched a science-themed segment on The Daily Show (TDS) or The Colbert Report (CR) and remarked at how “spot on”...

    -- Read more on ScientificAmerican.com
  • In Praise of Proofs by Contradiction that Aren't 28/08/2014 13:00
    If you don't know what to do, do something. That's one of my mottos when I teach math (and it's probably good life advice too). Last year, I taught introductory analysis (basically calculus with the...

    -- Read more on ScientificAmerican.com
  • Readers Respond to "A Crisis In Physics?" 23/08/2014 16:15
    Letters to the editor from the May 2014 issue of Scientific American

    -- Read more on ScientificAmerican.com
  • What Is the Goal of a Math History Class? 22/08/2014 13:30
    I'll be teaching a math history class for the first time this semester. I'm excited to be teaching it, but I've noticed that preparing for this class has been very different from preparing for other...

    -- Read more on ScientificAmerican.com
  • Science Media Beset with Gender Gaps 21/08/2014 20:52
    In the fall of 2005, I and a couple hundred other new students at Columbia University's journalism school walked into a lecture hall for a series of welcome speeches, and two things happened that...

    -- Read more on ScientificAmerican.com
  • Physics Week in Review: August 16, 2014 16/08/2014 10:21
    This week on Virtually Speaking Science, I chatted with astrophysicist Katie Freese, author of a new book, The Cosmic Cocktail: Three Parts Dark Matter.

    -- Read more on ScientificAmerican.com
  • Iranian Woman Nabs Highest Prize in Mathematics 13/08/2014 19:00
    Maryam Mirzakhani is among four young researchers to win the 2014 Fields medals, which are awarded every four years

    -- Read more on ScientificAmerican.com
  • Diversity in Focus at Upcoming Science Writers Meeting 12/08/2014 22:49
    Calling all journalists, authors, editors, producers, public information officers, students and communicators with a passion for science, tech, engineering and mathematics!

    -- Read more on ScientificAmerican.com
  • How to Talk About the Fields Medal at Your Next Cocktail Party 11/08/2014 18:08
    On Wednesday, four mathematicians will receive the prestigious Fields Medal at the International Congress of Mathematicians (ICM) in Seoul.

    -- Read more on ScientificAmerican.com
  • The Glory of Math Is to Matter 11/08/2014 13:00
    In 1842, when the famed German mathematician Carl Gustav Jacobi was invited to speak to a scientific meeting in Manchester, he had a surprise in store for his English hosts.

    -- Read more on ScientificAmerican.com
  • Skulls, Bloodletting, and How to Teach Science 07/08/2014 17:44
    [View the story "Skulls, Elephants and How To Teach Science" on Storify]

    -- Read more on ScientificAmerican.com
  • What will the future of education look like? 06/08/2014 12:00
    Scientific American's August supplement takes a look at the changing landscape of education in the face of emerging technology, and asks the question, how do we increase interest and engagement in...

    -- Read more on ScientificAmerican.com
  • What predicts NBA success? 06/08/2014 02:28
    “To an outsider watching Pop Herring’s basketball tryout in November 1978, it would not have been obvious that the gym at Laney High in Wilmington, N.C., held a player destined to become...

    -- Read more on ScientificAmerican.com
  • Physics Week in Review: August 2, 2014 02/08/2014 10:36
    Looking for a few good popular math books? In the latest New York Times Book Review, I look at five terrific recent ones: Jordan Ellenberg's How Not to Be Wrong, David J.

    -- Read more on ScientificAmerican.com