Thursday, March 23, 2023



Fun fact: The number 163 is prime, which we can prove simply by showing that it is not divisible by 2, 3, 5, 7, or 11.  (Of those prime factors, the only one that's a little tricky to check is 7, but I can see that since 140 + 21 = 161 is a multiple of 7, the number 163 is not.). By the way ... why don't I have to check prime factors greater than 11?  Howie Hua gives a nice little video explanation.


First, indulge me while I give a little plug for my own playful math project, a series of free math songs on my YouTube channel called Tunes that Count. We just released a new song about powers of 2 called The Power of Powers.  Check it out!

Now, check out the great things I found below.  Some are perfect little nuggets for use in classrooms or homeschooling. I also found some great math-art project ideas. Enjoy! 




March 14 was Pi Day, of course, but according to UNESCO it is also the International Day of Mathematics. One of the activities that was organized was a mathematics cartoon contest. Children and adults from all over the world entered, and you can see some of the selected cartoons in this gallery. Since the cartoons have no words -- only visuals and mathematical symbols -- the gallery is a testament mathematics as a universal form of communication. Below is one of my favorite of the cartoons, submitted by two students from Colombia.



Speaking of playful math....The French Ministry of Education sponsors a "week of mathematics" each year with a different theme in which it encourages people to create and share playful mathematics activities. This year, the "week" of mathematics ran from March 6 to March 15 and had the theme "Mathématiques à la carte." The contribution shown below is a clever game of vector dominoes by Jeux 2 Maths. For more details and for more games see their website. (Many of the games are so visual that you don't need to read French to understand them.) If you want to see more ideas, search for the hashtag #SDM2023 on Twitter.


NCTM reminded us with a tweet that March 20, 2023 was a palindrome day!  Naturally that raises questions. I wonder how special that is?  Do we get only one per year?  Do we get one every year? 



Math for Love

A recent post from Math for Love helps teachers out with resources to plan a Family Math Night at their school. In general, I love games and puzzles where the rules are simple but the math is not. This blog post offers a nice sample of such games and puzzles. The image below shows one puzzle type (The Broken Calculator), which I think would be perfect for 4th or 5th grade. In fact, I loved the idea so much I created my own version for a 5th grade decimal unit. (For example, how would you make 0.364 without the decimal point and without a 3, 6 or 4? Tricky!) 


Denise Gaskin's Let's Play Math

Denise has been sharing free games and activities from her collection of playful books. One of her books is called "Thinking Thursday: A new math journaling prompt every week!" From this book Denise recently shared the prompt, "Pick a topic you have learned in math. Write two correct statements and one false statement. Trade with a friend. Can you find each other’s fibs?" 


Here's an example of a more targeted prompt: "Tell me two truths and a lie about the median of a set of 5 numbers." If you try it yourself, as I did below, you'll see it's not so easy to write these kinds of statements. Open-ended tasks like this are great for differentiation within a classroom because students will each challenge themselves at an appropriate level.


A.          The median of 5 numbers is always a number in the set.

B.          The median of 5 numbers is always greater than the smallest number in. the set.

C.          The median of 5 numbers does not change if you add 10 to the largest number.

Reflections and Tangents: Thoughts on Math, Education, and Technology

The Reflections and Tangents blog has done a series of posts using what they call the "Same and Different inquiry routine." The idea is that you present students with two similar mathematical situations, and (as the name suggests) ask students to brainstorm how the situations are the same and how they are different. The March 3 blog post gives an example from calculus, but you could really adapt the structure of the activity to any grade level at all. For a middle school classroom, you might ask, for example, what is the same and what is different about 3 different sequences.  


7, 10, 13, 16, . . .

3, 6, 9, 12, 15, . . .

3, 9, 27, 81, . . . 


This recent tweet by Sunil Singh sort of blew my mind. He shows a textbook illustration that extends Pascal's triangle upwards to include Row - 1, Row -2, and Row -3. Why didn't I think of this before? Extending the triangle would make a wonderful, playful activity for middle schoolers. For older students, it broadens the application of the binomial theorem to include negative exponents. 



Playful Bookbinding and Paperworks

This blog is by an artist (Paula Beardell Krieg) who explores mathematics visually.  In a recent post she turns a circle theorem about inscribed right triangles into an art project.  Notice the visual impact of this drawing: In spite of the complexity and asymmetry of the drawing, many of the lines Paula created intersect in what appears to be the center of the circle. The drawing invites you to wonder why!

Julia Robinson Mathematics Festival activities blog

The Julia Robinson Math Festival is always a good source of playful activities. Their new blog for activities that are not quite ready for prime time is a great find. The most recent post on Modular Origami with Sonobe Units is a rich activity that could keep a math circle busy and engaged for a few sessions. The origami squares become building blocks to create polyhedra, which can then be explored geometrically (exploring structures) and algebraically (exploring numerical patterns). 

Early Family Math

Early Family Math is a resource for playful math activities for families and teachers.  Their recent  Puzzle of the Week is one that I know and love and had forgotten about. 

The idea is so simple.  How many non-overlapping squares can you divide a square into?  What's interesting about the puzzle is that it can be done as a straightforward exploratory exercise with young children. But it can also lead to an informal proof by mathematical induction. For example, I can see below that it is possible to turn 4 squares into 7 squares simply by subdividing one of the squares. But that technique can also be generalized. If I can make 4, then I can make 4 + 3 by subdividing one of the little squares. I can also make 4 + 3 + 3, or 4 + 3 + 3 + 3, and so forth. In fact, I can make any number of the form 4 + 3N  for N greater than or equal to 0.  What other patterns can you find?  Is there some largest number that can't be made?

This tweet from the prolific @sonukg4india caught my eye. It gives a beautiful demonstration of the Pythagorean theorem. This one shows a 3-4-5 triangle. What other Pythagorean triples could you build out of blocks in this way?  




BLOG CARNIVAL #163....LET'S GO! Fun fact: The number 163 is prime, which we can prove simply by showing that it is not divisible by 2, 3...