Sunday, July 24, 2016

Math Teachers at Play #100 - (Blog Carnival)

Wow, the 100th Math Teachers at Play! Such an honor to put together this milestone edition. Thanks to Denise Gaskins for creating and managing this great resource. Let her know if you are interested in hosting in the future.

I asked the 3J's for observations and facts about 100:
  • It is written with a 1 and two 0s
  • Square number (10 x 10)
  • It is a sum of two squares 64 + 36
  • It is a sum of two primes in several ways: 97 + 3, 89 + 11, 83 + 17, 71 + 29, 53 + 47
  • 1100100 in binary
  • 100 has 9 factors, which sounds like a lot, but is not an anti-prime
  • 100 is the start of a 26 term Collatz Sequence: 100, 50, 25, 76, 38, 19, 58, 29, 88, 44, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1 (little program for Collatz play)
Number Gossip revealed that it is a practical, powerful, happy, odious number. Hmm, a jolly dictator?

Here's a very familiar 100 in our daily life:

Unfortunately, this 100 makes far fewer appearances:

A 100 puzzle

To get started, here's a tricky puzzle that, semi-famously, has been a Google interview question. This phrasing comes from Good Riddles Now:
There are 100 prisoners lining up to go to jail. Each prisoner is wearing a hat that is either black or white. The prisoners don't know their own hat color, just the hat color of those in front of them in line (the first prisoner in line can't see anyone's hat and the last prisoner can see everyone's hat except their own). Starting from the back, one of the guards asks each prisoner what color their hat is. If they are correct they get to go free but if they are wrong they go to jail. 
If the prisoners get to discuss a plan, how can at least 99 of them be saved?
Talking about math
I blended ages here because I've noticed a lot of great cross-age pollination. The little ones are often very engaged and surprisingly insightful on topics that seem much more mature, while elementary conversations often touch some deep concepts.

AO Fradkin and her daughter discussed "how long is 3 minutes?" Hard to get deeper than the nature of time and how our perception depends on context (or does it?)

A view of Fermat's role in Fermat's Last Theorem from Mathematical Enchantments that nicely touching the fact of changing tastes in mathematical research. What mathematical preferences do you and your kids have?

Some tidbits for the Math is Everywhere meme:

  1. Using big data to analyze story arcs.
  2. Life through a Mathematician's Eyes has two posts on What a Mathematician should see in Amsterdam and Visiting Amsterdam like a Mathematician
I can never resist an icosahedron picture and there's a nice one in the first Amsterdam post:

Enjoy a joke anecdote about mathematical precision from Curiousa Mathematica. I like to tell elementary kids these kinds of jokes and see how they respond. It is a delight when they get it, but I also like to laugh at their deadpan expressions when they don't understand. 

Finally, a great way to start talking about math is to do math where you'll be seen doing it. This might require an emergency math kit (from Solve My Maths.)

Crafts and Constructions
Generally, these are accessible to young children, but also have some deep mathematics that offer something for any of us to explore.

Something our kids recently made: Flextangles craft activity (3d flexagons)

We love optical illusions and Sugihara's Illusion is a fantastic one. This post gives an explanation, then the next provides a printable. Agamographs are an accessible craft with a similar idea (instructions on Babble Dabble Do).

Benjamin Leis writes about an eye-catching decomposition and recomposition puzzle to start some exploration: hinged polygons.

Kira Zelbo offers up a free booklet that introduces isometric dot paper for drawing and visualizing three dimensional forms: Spatial Learning. Education Realist recently documented his experience using isometric grid paper with his class in Great Moments in Teaching.

Elementary Explorations and Middle School Mastery

Denise Gaskins (have you heard of her?) stimulates a discussion of favorite puzzle books in her review of Lilac Mohr's Math and Magic In Wonderland.

AO Fradkin again, helping some early elementary kids in discovering the triangle inequality.

John Golden serves another ace with his Wimbledon Game.

An old post from Sue Downing caught my attention: these place value cups are a great idea and make me think (fondly) of combination bike locks.

Addition Boomerang is a Mathpickle activity we played recently with our 1st-4th graders. When can you make 100? With that target, of course we had to include it in this MTaP!

Math Minds has ants-on-the-brain in 100 hungry ants. Trust me, it is better than ants in the pants.

Second graders explore proofs based on a geometric investigation: Squarable Numbers

Another post from Sue Downing that came in handy recently: "Is that all there are?" Multiplication facts. Now that you know the multiplication facts aren't scary, get some practice by playing with 
anti-primes (Numberphile). We got a lot of value out of seeking the anti-prime (er, highly composite number) that follows 24.

Number bracelet investigation. Our school and family have looked at this several times. Another great extension is to work in bases other than 10. Another way to understand it is working modulo 10 (or whatever integer you choose to set to 0).

Baseball, with its large collection of player and team stats, offers a natural entry point for mathematical conversations. Mashup Math walks through some examples in Mathematics of Major League Baseball. For a related take on this idea, see Mathpickle's Introducing Stats to Younger Children.

High School Adventures

Mrs E shares a lesson plan focused on getting kids to analyze and critique advertisements at Mrs E Teaches Math. An important life skill on its own and Mrs E sees it as a helpful bridge into writing proofs.

What happens when you are living inside a word problem? Math in real life.

I don't think this is a recent addition from Dan Meyer, but his Finals Week three-act seemed more fun to do during summer, away from the normal stresses of the school year.

There are some elementary and sophisticated ways to think about divisibility rules. In this post Curious Cheetah hits a bunch at one time.

"Stoichiometry is the math of chemistry," according to Amy Roediger. Here is her explanation and a discussion of teaching methods, parts 12, and 3

Manan Shah contributes his approach to dealing with Annoying Function Notation. Can you make sense of these contrasting pairs:

Also, make sure to check out Manan's curation of the latest Carnival of Mathematics.

Po Shen Lo and Mike Lawler: a great combination... and Mike gives us two posts with PSL (first and second)!

Step into some difficult probability, statistics, and forecasting with Big Thompson Flood.

Singapore Maths Tuition walks us through a vector calculation to find the foot of a perpendicular from a point and to a line.

Ben Vitalis has a constant stream of interesting challenges, most accessible to algebra students: Odds equal Evens.

Puzzling Recreations

Math Arguments makes a surprising re-appearance to post a nice probability dice from Ben Orlin.

Lisa Winer (star of the 99th MTaP) talks about her plexer puzzles. Aside from being fun, these are a good place to practice Notice & Wonder.

Our family has recently become fans of the Futility Closet podcast, especially their lateral thinking puzzles.

Reminder: one great thing to do with any puzzle is CREATE YOUR OWN!!!

Teaching Tips

Which one doesn't belong (WODB) is a great format for a rich discussion. has a really nice collection of mathematical WODBs. I was reminded of this resource by this delightful WODB of WODB from John Golden.

Joe Schwartz continues a MTBoS theme of getting fixes for worksheets.

Amy Roediger put together a good collection of resources as she prepared to lead a
coding camp. A Recursive Process has a further discussion of the links between coding and math, including some more resources.

The folks at the Mind Research Institute have put together a summer reading list of 9 Enlightening Summer Reads for Math Teachers. The list mixes sci-fi and books about teaching. If you don't know the Mind Research Institute, they are behind/linked with ST Math, an on-line elementary grades math system that I really like. I had the opportunity to trial their system years ago and recently went through their free demo.  Now, if only someone there would be willing to get in touch and tell me how I could subscribe for my kids to use .....!

Twitter Math Camp 2016 was just held and there are a lot of math teachers blogging about their experiences. If the posts I've gathered above aren't enough for you, I suggest hitting J Fairbanks's blog 8 is My Lucky Number for 10 (wow!) posts about the convention and further links.


  1. Wonderful carnival post! Thank you so much for hosting. :)

  2. Hi Joshua!
    Thank you for the link and mention about ST Math. I am excited to let you know that ST Math is available for purchase for homeschoolers at I am sorry that we did not communicate this to you sooner!

    If you have any questions, feel free to let me know.

    -Calli Welsch, Communications Specialist,

  3. Hi Joshua!

    I wanted to check in and ensure that we helped you get what you needed regarding ST Math. The best way to get more information via phone is (888)751-5443 or via email is

    Thank you for your time!

    -Calli Welsch, Communications Specialist,