How Will You Celebrate this Epic Twosday?

Tomorrow is Tuesday 2/22/22 (or 22/2/22, if you prefer). What a wonderfully epic Twosday!

Here’s a puzzle your family or class may enjoy…

The “All 2s” Challenge

Use only the digit 2, and try to use as few of them as you can for each calculation. You may use any math operations you know.

For example:
0 = 2 − 2
8 = 2 + 2 + 2 + 2

  • Can you find a way to make 8 using fewer than four 2s?
  • What other numbers can you make?
  • Can you calculate all the numbers from 1–20? 1–100?

Putting 2 in Perspective

You might enjoy practicing your math art skills with this 2-digit challenge from Steve Wyborney.

How many blocks make the digit 2? How did you count them?

Playful Math #152: Auld Lang Syne Edition

Welcome to the 152nd edition of the Playful Math Education Blog Carnival — a smorgasbord of delectable tidbits of mathy fun. It’s like a free online magazine devoted to learning, teaching, and playing around with math from preschool to high school.

Bookmark this post, so you can take your time browsing. There’s so much playful math to enjoy!

We didn’t have a volunteer host for January, so I’m squeezing this in between other commitments. This is my third no-host-emergency carnival in the last year, which is NOT sustainable. If you’d like to help keep the Playful Math Carnival alive, we desperately need hosts for 2022!

By tradition, we start the carnival with a puzzle or activity in honor of our 152nd edition. But if you’d rather jump straight to our featured blog posts, click here to see the Table of Contents.

Math Journaling with Prime Numbers

Cool facts about 152: The eighth prime number is 19, and 8 × 19 = 152. When you square 152, you get a number that contains all the digits from 0–4. You can make 152 as the sum of eight consecutive even numbers, or as the sum of four consecutive prime numbers.

But 152 has two real claims to fame:

  • It’s the smallest number that is the sum of the cubes of two distinct odd primes.
  • And it’s the largest known even number you can write as the sum of two primes in exactly four ways.

So here’s your math investigation prompt:

  • Play around with prime numbers. Explore their powers, their sums, and anything else about them you like.
  • What do you notice? What do you wonder?
  • What’s the most interesting number relationship you can find?

Continue reading Playful Math #152: Auld Lang Syne Edition

Did You Get Your Puzzle Calendar?

Earlier this week, I sent out my last Playful Math Newsletter to email subscribers.

Most months, my newsletter includes tips and activity ideas for playing math with your kids. But from time to time, I give away a free sample of whatever I’ve been working on — an early draft of something that will eventually show up in one of my books or printable activity guides.

This month’s gift was a Pentomino Puzzle Calendar, a daily adventure in spatial reasoning.

(If you’re a subscriber, be sure to check your inbox!)

For those who haven’t signed up yet, follow this link for more information:

Join Our Playful Math Email Newsletter

And if you hit “Reply” to your welcome email and ask for a printable Pentomino Puzzle Calendar of your own, I’ll send you one right away.

Playful Math Journaling: Preorder on Kickstarter

Are you looking for new ways to explore math with your kids?

Would you like an easy, no-prep resource for creative problem-solving, number play, math art, word problems, mini-essays, math poetry, geometry investigations, research projects, and much more?

I’ve just launched a Kickstarter project for people to preorder my new book, 312 Things To Do with a Math Journal. It just might transform your child’s experience of math.

In a math journal, children explore their own ideas about numbers, shapes, and patterns through drawing or writing in response to a question. Journaling teaches them to see with mathematical eyes. Not just to remember what we adults tell them, but to create their own math.

Scroll down the Kickstarter project page to download the free 16-page printable “Math Journaling Sampler” file. It includes one of my all-time favorite math activities.

If you like what you see, I’d love to have your support. The more people we can get to share the project in the early days, the more likely Kickstarter will join in and promote it to new readers.

Have fun playing math with your kids!

Visit the Playful Math Journaling Kickstarter page

Playful Math Education Carnival 147

Welcome to the 147th edition of the Playful Math Education Blog Carnival — a smorgasbord of delectable tidbits of mathy fun. It’s like a free online magazine devoted to learning, teaching, and playing around with math from preschool to high school.

Bookmark this post, so you can take your time browsing. There’s so much playful math to enjoy!

By tradition, we start the carnival with a puzzle in honor of our 147th edition. But if you’d rather jump straight to our featured blog posts, click here to see the Table of Contents.

Continue reading Playful Math Education Carnival 147

New! Your Student Can Be a Math Maker

When children create their own math, they build a deep understanding of mathematical concepts and relationships.

And it’s fun!

So take a break from your normal math program to play with creative math. Students can:

Check Out the Gallery

We have a few entries already in the Student Math Makers Gallery.

Click Here To Visit the Gallery

Join the Student Math Makers

We’d love to add your students’ math to our collection and share it with viewers all around the world!

To submit a math creation, download a Math Makers Invitation and Submission Form below:

CREDITS: “Creating Math Puzzles by Sian Zelbo, the author of Camp Logic, via NaturalMath.com.

Playful Math Carnival 144: Anniversary Edition

Welcome to the 144th edition of the Playful Math Education Blog Carnival — a smorgasbord of delectable tidbits of mathy fun. It’s like a free online magazine devoted to learning, teaching, and playing around with math from preschool to high school.

Bookmark this post, so you can take your time browsing.

There’s so much playful math to enjoy!

By tradition, we would start the carnival with a puzzle/activity in honor of our 144th edition. But this time, I want to take a peek back at the history of our carnival.

But if you’d rather jump straight to our featured blog posts, click here to see the Table of Contents.

Continue reading Playful Math Carnival 144: Anniversary Edition

Math Puzzle from the Ancient Kingdom of Cats

It may look like Cimorene has lain down on the job, but don’t be fooled! She’s hard at work, creating a math investigation for your students to explore.

Cats know how important it can be for students to experiment with math and try new things. Playing with ideas is how kittens (and humans!) learn.

Cimorene wants you to know that the Make 100 Math Rebels Kickstarter offers a great way for human children to learn math through play. She encourages you to go watch the video and read all about the project.

Too often, school math can seem stiff and rigid. To children, it can feel like “Do what I say, whether it makes sense or not.” But cats know that kids are like kittens — they can make sense of ideas just fine if we give them time to play around.

So Cimorene says you should download the free sample journaling pages from the Math Rebels Kickstarter page. The beautiful parchment design makes doing math an adventure.


[The free download will always be there, even after the Kickstarter project ends.]
Make 100 Math Rebels Kickstarter

Cimorene’s Puzzle Challenge

Cimorene’s math puzzle is a classic geometry problem from the ancient Kingdom of Cats: Squaring the Circle.

Draw a circle on your journal page. Can you draw a square (or rectangle) that has the same area?

How would you even begin such a task?

Notice Cimorene’s hint in the photo above: Try drawing the square that just touches the edges of your circle. (We call those just-touching lines “tangents” to the circle.)

  • What do you notice? Do the square and the circle have the same area? How close are they?

The tangent square sets an upper limit on the area of the circle. You can see that any square that exactly matches the circle would have to be smaller than the tangent square.

  • Can you find a square that sets a lower limit on the area of the circle? That is, a square that must have less area than the circle?
  • What’s the biggest square you can draw inside your circle? Can you find a square that has all four corners on the circle?

We call that biggest-inside square “inscribed” in the circle. Any polygon whose corners all sit on the circle is an inscribed polygon.

  • Play around with circles and squares. How close can you get to matching their size?

Further Exploration

After you have explored for awhile on your own, Cimorene has one more twist in her puzzle.

In the ancient Kingdom of Cats, the wise ones estimated the area of a circle this way:

Divide the width of the circle in thirds, and then in thirds again. (That is, cut the diameter into nine parts.) Draw a square with sides measured by eight such parts.

You can try this on your journaling page by drawing a circle that is nine squares wide. Then draw a square overlapping it, with sides that are eight squares in length.

  • How closely do the areas match?

Playing with Pi

Here’s a surprise: Cimorene’s puzzle isn’t really about squares, but about calculus.

The problem of Squaring the Circle is really a much bigger question: Finding the area of a square, rectangle, or other polygon is relatively easy, but how can we discover the area of a curved shape?

For a circle, the area is related to the number pi, which is the number of times you would have to walk across the circle to equal the distance of one time walking around it.

graphic by John Reid (cc by-sa 3.0)

graphic by John Reid (cc by-sa 3.0)
So the problem of Squaring the Circle is really the same as asking, “What is the value of pi?”

  • Can you figure out what approximate value for pi matches the 8/9 square used in the ancient Kingdom of Cats?

If you’d like to learn more about pi, get ready for a celebration: Pi Day is coming soon! Every year, millions of children celebrate math on March 14th, because if you write the date as 3/14, it’s the same as the first three digits of pi.

Find out more about playing with pi in my Pi Day Round-Up post.

You may also enjoy:

Share Your Stories

Cimorene would love to hear about your children’s experiences playing with math! Please share your story in the comments below.

Can You Do the Math Salute?

Did your device hide the video? Find it on YouTube here.

How Is This Math?

The idea that math is only about numbers, calculations, and textbook exercises is one of the greatest lies we learn in school. Of course, nobody ever comes straight out and actually says that. But the whole system teaches us every day what counts for math and what doesn’t.

James Tanton’s math salute is a physical puzzle.

How in the world did he do that?

Physical puzzles don’t fit into our cultural understanding of math. But the process of figuring out the puzzle is the same problem-solving process we use to figure out other puzzles — including the puzzles we call math.

In fact, real mathematics is all about figuring out puzzles without a teacher showing you what to do. Problem-solving is a universally useful skill.

As master teacher W. W. Sawyer said:

“Everyone knows that it is easy to do a puzzle if someone has told you the answer. That is simply a test of memory. You can claim to be a mathematician only if you can solve puzzles that you have never studied before. That is the test of reasoning.”

—W. W. Sawyer, Mathematician’s Delight

So tackle the puzzle of the math salute. Show it to your kids. (And don’t be surprised if they figure it out before you do!)

[THE FINE PRINT: I am an Amazon affiliate. If you follow the link and buy something, I’ll earn a small commission (at no cost to you). But this book is a well-known classic, so you should be able to order it through your local library.]

New Printable Puzzle Books: Diffy Inception

The best way to practice math is to play with it—to use the patterns and connections between math concepts in your pursuit of something fun or beautiful.

Diffy Inception puzzles have their own symmetric beauty, but mostly they are just plain fun. Students can practice subtraction and look for patterns in the difference layers.

I just published four new activity books to our online store:

Notes to the teacher include puzzle instructions, game variations, journaling prompts, and more. Plus answers for all puzzles.

Available with 8 1/2 by 11 (letter size) or A4 pages.

Click for a Preview

My publishing company runs this online store, so you can find all my playful math books there — including an exclusive pre-publication ebook edition of my newest title, Prealgebra & Geometry: Math Games for Middle School. Click here to browse the Tabletop Academy Press store.