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
  • Uber, but for Topological Spaces 01/03/2015 01:00
    So it's cold and rainy, and you're up a little too late trying to figure out why that one pesky assumption is necessary in a theorem. Wouldn't it be nice if you could just order up a space that was...

    -- Read more on ScientificAmerican.com
  • Things to Make and Do in the Fourth Dimension (Book Review) 26/02/2015 23:00
    Sometimes you want to learn a “new” multiplication algorithm from a general interest math book, sometimes you want to learn why voting systems are doomed to imperfection, and...

    -- Read more on ScientificAmerican.com
  • Game Theory Calls Cooperation into Question 23/02/2015 19:00
    A recent solution to the "prisoner's dilemma," a classic game theory scenario, has created new puzzles in evolutionary biology

    -- Read more on ScientificAmerican.com
  • It's Time for More Racial Diversity in STEM Toys 23/02/2015 18:00
    It’s clear that we as a nation are failing to engage minority students in science, technology, engineering, and mathematics as well as we could.

    -- Read more on ScientificAmerican.com
  • 15 Surprises about Scientific American 22/02/2015 17:52
    Scientific American's parent company, Macmillan Science & Education strives to be both a place where curious minds gather together to achieve great things for our customers—and where we...

    -- Read more on ScientificAmerican.com
  • Physics Week in Review (Valentine’s Edition): February 14, 2015 14/02/2015 10:43
    Today is Valentine’s Day. In love? Or just the opposite? Express how you feel with physics-inspired Valentines—and anti-Valentines for those who perhaps aren’t huge fans of the...

    -- Read more on ScientificAmerican.com
  • Is AI Dangerous? That Depends… 13/02/2015 16:38
    Somewhere in the long list of topics that are relevant to astrobiology is the question of ‘intelligence’. Is human-like, technological intelligence likely to be common across the universe?

    -- Read more on ScientificAmerican.com
  • Gauss and Germain on Pleasure and Passion 13/02/2015 13:30
    Sophie German, who was not allowed to attend university, was the first woman to make significant original contributions to mathematical research.

    -- Read more on ScientificAmerican.com
  • How to Choose the Form of an Infographic: It's All about Context 10/02/2015 14:00
    As a graphics designer, I have a love/hate relationship with circles. The humble form provides a relief from rigid rectangular chart structures that are pinned to x- and y-axes.

    -- Read more on ScientificAmerican.com
  • Strange Stars Pulsate According to the "Golden Ratio" 09/02/2015 14:30
    Astronomers have discovered variable stars that periodically dim and brighten at frequencies close to the famed golden mean

    -- Read more on ScientificAmerican.com
  • Cities Could Win Economically by Losing Olympics 06/02/2015 18:00
    According to sports economist Andrew Zimbalist, most cities that win the right to host the Olympics will spend far more to prepare for the games than they estimate in their winning bid. Steve Mirsky...

    -- Read more on ScientificAmerican.com
  • The Media and the Genius Myth 05/02/2015 14:00
    I’ve been thinking a lot about the genius myth, the notion that in order to be a successful in certain disciplines, you need to have a special innate talent that can’t be learned.

    -- Read more on ScientificAmerican.com
  • Understand the Measles Outbreak with this One Weird Number 31/01/2015 21:21
    15. That’s all you need to know about the measles. OK, that’s not true at all. There's no one weird trick that will give you a flat belly (besides lying face-down on something flat), and...

    -- Read more on ScientificAmerican.com
  • Does Mathematical Ability Predict Career Success? 29/01/2015 20:00
    A study that has tracked students exceptional in math for 40 years checks their accomplishments

    -- Read more on ScientificAmerican.com
  • Apply for Science Communication Awards, Fellowships and Internship Programs 29/01/2015 13:12
    Participation of broader audiences in science, technology, engineering, mathematics (STEM) requires engaging under-served audiences. The conduit of this engagement is communication.

    -- Read more on ScientificAmerican.com
  • 3 Super Bowl Fun Facts 28/01/2015 13:00
    Want to amaze your friends at that Super Bowl party you're going to? All you have to do is hit 'em with some Super Bowl math fun facts. Keep on reading to learn what they are!

    -- Read more on ScientificAmerican.com
  • Genetic Memory: How We Know Things We Never Learned 28/01/2015 12:00
    I met my first savant 52 years ago and have been intrigued with that remarkable condition ever since. One of the most striking and consistent things in the many savants I have seen is that that they...

    -- Read more on ScientificAmerican.com
  • Learn to Count like an Egyptian 26/01/2015 13:30
    Last semester, I began my math history class with some Babylonian arithmetic. The mathematics we were doing was easy—multiplying and adding numbers, solving quadratic equations by completing...

    -- Read more on ScientificAmerican.com
  • Battling Bees and Future Bridge Designs: <i>Scientific American</i>'s February Issue 25/01/2015 19:00


    -- Read more on ScientificAmerican.com
  • Super-Gifted Boys Choose Higher-Powered, Higher-Paying Careers Than Female Peers 23/01/2015 14:15
    A classic gender divide persists even among people who scored as 11- to 13-year-olds in the top 1 percent in the U.S. on the SAT

    -- Read more on ScientificAmerican.com
  • Attempts to Predict Terrorist Attacks Hit Limits 20/01/2015 22:30
    Erratic human behavior and incomplete information plague efforts to model this risk

    -- Read more on ScientificAmerican.com
  • Martin Luther King Jr.’s Haunting Reflections on Science and Progress 19/01/2015 18:50
    Wanting to post something to honor Martin Luther King Day, I searched online for commentary by King on science. I found some examples in a terrific 2012 column by science journalist Cara Santa Maria,...

    -- Read more on ScientificAmerican.com
  • Science and Art Exhibits To Launch 2015 12/01/2015 19:40
    The number of exhibits combining science and art in some capacity has grown steadily since I began blogging about them in 2011. With exhibits in galleries and museums across the country,...

    -- Read more on ScientificAmerican.com
  • Game Theorists Crack Poker 08/01/2015 21:52
    An "essentially unbeatable" algorithm for Texas hold 'em points to strategies for solving real-life problems without having complete information

    -- Read more on ScientificAmerican.com
  • Shape Science: Play-Doh Math 08/01/2015 16:00
    A volume-based venture from Science Buddies

    -- Read more on ScientificAmerican.com