If there are 14 people in a group, and each shakes hands with each other, there will be 91 handshakes. (Can you see why?)
91 = 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13
(which makes it triangular)
91 = 7 * 13
(the middle and last numbers in the sum above)
Will this always happen for triangular numbers?
Games & Puzzles
- Shannon Duncan, a 6th grade math & science teacher, shares 4 Reasons to Promote Math Success through Games at the MIND Research Institute blog, illustrating her ideas with some of the games she has her students playing. I especially like the first point - making a mind-body connection.
- John Golden (@mathhombre) shares Angle of Coincidence at his blog, Math Hombre, about an angle identification game he's developing. Ask your students to playtest it and give him feedback! John also wrote about the start of the semester, and included a game called In or Out? that looks fun.
- Jeff Trevaskis shares a Multiplication Tic-Tac-Toe Game at his blog, webmath.
- Carole Fullerton shares Number Tile Puzzles at her blog, Mathematical Thinking.
- Gray Antonick interviewed Paul Salomon in the New York Times Numberplay column, about his Imbalance Puzzles, one of many puzzles and games featured in Playing with Math: Stories from Math Circles, Homeschoolers, and Passionate Teachers (my book, published in April!).
- Denise Gaskins (@letsplaymath) shares an old favorite, 30+ Things To Do with a Hundred Chart, at her blog, Let's Play Math.
- Brian Bushart (@bstockus) shares Fraction Number Sense at his blog, Teaching To the Beat of a Different Drummer.
- Lior Pachter shares Unsolved math Problems and the Common Core at his blog, Bits of DNA. (Lior writes about computational biology. I found this post thanks to Andrew Knauft, at LimSoup.)
- Stephen Cavadino (@srcav) shares Parallelograms at his blog, cavmaths, on a student's creative way to find the area of a parallelogram.
- Ioana I Pantiru (@LThMathematics) shares Playing with Paper Folding at her blog, Life Through a Mathematician's Eyes, showing the steps of an origami construction. In her post, Maths Class Everywhere, she asks readers to take her survey of math classes around the world.
- Curmudgeon shares Circles on a Lattice, at their blog, Math Arguments 180. I wonder if this would make a good problem for a math circle...
- Greg Blonder, a professor of manufacturing and product design, shares Trisecting the Angle With a Straightedge, at Plus Maths.
- There have been lots of posts in the past few months about classifications of pentagons (here's one), because a new (15th) type of pentagon that will tile the plane was recently found. Here's a good background post, from before the discovery, from the Mathematical Tourist.
It's All Connected
- Miss D shares The Age of Ultron at her blog, Miss D the Teacher, about teaching a unit on artificial intelligence in a way that gets at the deep ideas and really gets students thinking, partly through connecting math, science, and art.
- Henri Picciotto (@hpicciotto) posts about Computer Programming and Math Education.
- What is the distance to Mars? It changes depending where the two planets are in their orbits. John D. Cook explains the math.
- Michelle shares Making Time for the Serendipitous at The Rookery.
Ideas for Learning ...
- Kate Snow (@katesmathhelp) shares How to Teach Your Kids to Read Math at her blog, Kate's Homeschool Math Help. I'm still trying to teach my college students how to read math, with some of the same tips.
- Manan (@shalock) shares Becoming Mathematically Fluent at his blog, Math Misery.
- Shecky (@sheckyr) shares True Deep Beauty ... at his blog, Math-Frolic, about the how our understanding of math deepens.
- Chris Rime is making monthly math calendars (Algebra I, II, and Geometry), available as doc or pdf at his blog, Partially Derivative.
... And Teaching
- Tom Bennison (@DrBennison) shares How to enjoy your NQT Year at his blog, Mathematics and Coding. [I had to look up NQT. It means newly qualified teacher, and in England and Wales, you are "inducted" in your NQT year, (generally) your first year of paid teaching.] I like his suggestion to make time for doing some math(s) yourself.