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
  • Math Twitter Bots, Reviewed and Rated 28/07/2014 13:00
    In the course of being a math person on Twitter, I have run across some math-related Twitter bots and feeds. It would just be mean to grade my human tweeps, but I have no qualms about rating the bots!

    -- Read more on ScientificAmerican.com
  • Mysterious Tiles from a Time When Art and Science Were Friends 25/07/2014 17:44
    Forces in society of late have lots of us longing for the days of the Enlightenment, smallpox, powdered wigs, ridiculously uncomfortable clothing and all.

    -- Read more on ScientificAmerican.com
  • The Shocking Failure of British Rail Travel to Respect the Triangle Inequality 23/07/2014 13:00
    I spent about a month in the UK earlier this summer, and that meant I took a lot of train trips. I love riding trains: the feeling of endless possibility I get when I look at the departure boards,...

    -- Read more on ScientificAmerican.com
  • When was the last time you used a print dictionary? 22/07/2014 13:39
    I used to keep a small dictionary in my bedside table, another in the end table near the couch, one on my home office desk and another on my desk at work.

    -- Read more on ScientificAmerican.com
  • Tapping Your Inner Rain Man 21/07/2014 12:30
    A blow to the head can sometimes unmask hidden artistic or intellectual gifts

    -- Read more on ScientificAmerican.com
  • Adjunct Instructors Petition for Better Pay, Job Security 19/07/2014 03:23
    Note: We’re pleased to feature a guest post by former Cocktail Party Physics co-blogger Ann (Lee) Kottner. Jennifer has graciously given me space to ask for some help from the science writing...

    -- Read more on ScientificAmerican.com
  • Scientific American Editor Testifies at U.S. Senate [Video] 18/07/2014 05:17
    At a hearing on the future of federal research investment, a science magazine editor and three noted scientists asked the U.S. Senate to support basic research

    -- Read more on ScientificAmerican.com
  • Bioinformatics: Big Data Versus the Big C 11/07/2014 12:00
    The torrents of data flowing out of cancer research and treatment are yielding fresh insight into the disease

    -- Read more on ScientificAmerican.com
  • LEGO Reveals Female Scientist Minifigures 10/07/2014 16:55
    After much rejoicing at the news last month that LEGO would mass-produce a set of female scientist minifigures, the company has released a prototype of the final set to its original designer, Ellen...

    -- Read more on ScientificAmerican.com
  • Some Infinities Are Bigger than Other Infinities, and Some Are Just the Same Size 10/07/2014 12:00
    Warning: contains minor spoilers for The Fault in Our Stars. I recently read The Fault in Our Stars by John Green, now a major motion picture that has led to theft in Amsterdam and a shortage of...

    -- Read more on ScientificAmerican.com
  • Put Yourself in the Cheater's Shoes 09/07/2014 20:17
    Could seeing the world through the eyes of the scientist who behaves unethically be a valuable tool for those trying to behave ethically? Last semester, I asked my “Ethics in Science”...

    -- Read more on ScientificAmerican.com
  • The Magic of Number 9 (Part 2) 09/07/2014 12:15
    The number 9 is kind of amazing. How amazing? Keep on reading for the exciting conclusion to Math Dude's story about the magical number 9 

    -- Read more on ScientificAmerican.com
  • British Objects of Constant Width 04/07/2014 08:00
    As I wrap up a trip to the UK, I reflect on the many objects of constant width I encountered here. I’ll let Numberphile tell you a little more about objects of constant width.

    -- Read more on ScientificAmerican.com
  • The Magic of Number 9 (Part 1) 02/07/2014 12:15
    Have you ever noticed that the number 9 is kind of amazing? What's that…did I hear you say "NO?" Then prepare yourself to be amazed and keep on reading to learn all about the magic...

    -- Read more on ScientificAmerican.com
  • Jell-O Brains and DNA: High School Students Launch Innovative STEM Program 01/07/2014 20:00
    The following guest post is by Roy Rinberg, a graduate of Thomas Jefferson High School for Science and Technology in Alexandria, Va. and an incoming freshman at New York University. He is...

    -- Read more on ScientificAmerican.com
  • “Neuro Scout” Gets into Batters’ Heads to Rate Hitters 01/07/2014 13:00
    Columbia University start-up Neuroscout is developing a tool that would allow baseball and other sports teams to evaluate talent by examining players’ brain waves

    -- Read more on ScientificAmerican.com
  • Urban Science Adventure: 100+ things to do outside 30/06/2014 16:28
    It’s summer. The kids are out of school. You want to keep them engaged and active. Most parents also want to keep them on track academically, but not necessarily with a strong hand approach to...

    -- Read more on ScientificAmerican.com
  • Introduction to open peer review 28/06/2014 13:42
    Last post we talked about traditional peer review, which is at least single-blinded. This time we will focus on Open Peer Review (OPR). The narrowest way to describe OPR is as a process in which the...

    -- Read more on ScientificAmerican.com
  • The Most Mathematically Perfect Day of the Year 28/06/2014 11:28
    Whether you write it 6/28 or 28/6, today is a perfect day. A perfect number is a number that is the sum of its factors besides itself, and 6 (1+2+3) and 28 (1+2+4+7+14) are the first two perfect...

    -- Read more on ScientificAmerican.com
  • ScienceArt Exhibits Heat Up This Summer 27/06/2014 21:21
    Take a break from the heat this summer to step into some cool galleries exhibiting scienceart. If the exhibits keep pouring in at this rate, I’ll have to split up this post by region.

    -- Read more on ScientificAmerican.com
  • Why Tau Trumps Pi 25/06/2014 14:00
    A growing movement argues that killing pi would make mathematics simpler, easier and even more beautiful

    -- Read more on ScientificAmerican.com
  • 2, 4, 6, 8, What Does Not Associate? 23/06/2014 13:42
    Last month, I wrote about group theory via monkeys, and it got me thinking about the associative property. A mathematical group consists of a collection of stuff: integers, or rational numbers, or...

    -- Read more on ScientificAmerican.com
  • With Prizes Like This, Who Needs a Nobel? 23/06/2014 08:00
    Five mathematicians, working in a field spurned by the Nobel academies as a matter of course, will receive $3-million awards of their own

    -- Read more on ScientificAmerican.com
  • Quasicrystal Meteorite Exposes Novel Processes in Early Solar System 18/06/2014 15:14
    When scientists traced a museum rock back to its origins, they uncovered mysteries about the early solar system

    -- Read more on ScientificAmerican.com
  • 3 Frequently Asked Questions About Math Puzzles 18/06/2014 12:15
    Think of a number, add 3, double it, now subtract 4, divide by 2, and finally subtract your original number from the result. You get 1, right? How do I know? And what are some other fun math tricks...

    -- Read more on ScientificAmerican.com