## Celebrating Math with Pi Day

Are your students doing anything special for Pi Day?

Back when we were homeschooling, my kids and I always felt stir-crazy after two months with no significant break. We needed a day off — and what better way could we spend it than to play math all afternoon?

I love any excuse to celebrate math!

Pi Day is March 14. If you write dates in the month/date format, then 3/14 at 1:59 is about as close as the calendar can get to 3.14159etc.

(Otherwise, you can celebrate Pi Approximation Day on July 22, or 22/7.)

Unfortunately, most of the activities on teacher blogs and Pinterest focus on the pi/pie wordplay or on memorizing the digits. With a bit of digging, however, I found a few puzzles that let us sink our metaphorical teeth into real mathematical meat.

### What’s the Big Deal? Why Pi?

In math, symmetry is beautiful, and the most completely symmetric object in the (Euclidean) mathematical plane is the circle. No matter how you turn it, expand it, or shrink it, the circle remains essentially the same.

Every circle you can imagine is the exact image of every other circle there is.

This is not true of other shapes. A rectangle may be short or tall. An ellipse may be fat or slim. A triangle may be squat, or stand upright, or lean off at a drunken angle. But circles are all the same, except for magnification. A circle three inches across is a perfect, point-for-point copy of a circle three miles across, or three millimeters.

What makes a circle so special and beautiful? Any child will tell you, what makes a circle is its roundness. Perfectly smooth and plump, but not too fat.

The definition of a circle is “all the points at a certain distance from the center.” Can you see why this definition forces absolute symmetry, with no pointy sides or bumped-out curves?

One way to express that perfect roundness in numbers is to compare it to the distance across. How many times would you have to walk back and forth across the middle of the circle to make the same distance as one trip around?

The ratio is the same for every circle, no matter which direction you walk.

That’s pi!

### Puzzles with Pi

For all ages:

Sarah Carter created this fun variation on the classic Four 4s puzzle for Pi Day:

Using only the digits 3, 1, 4 once in each calculation, how many numbers can you make?

You can use any math you know: add, subtract, multiply, square roots, factorials, etc. You can concatenate the digits, putting them together to make a two-digit or three-digit number.

For older students:

1. Imagine the Earth as a perfect sphere with a long rope tightly wrapped around the equator. Then increase the length of the rope by 10 feet, and magically lift it off the Earth to float above the equator. Will an ant be able to squeeze under the rope without touching it? What about a cat? A person?

2. If you ride a bicycle over a puddle of water, the wheels will leave wet marks on the road. Obviously, each wheel leaves a periodic pattern. How the two patterns are related? Do they overlap? Does their relative position depend on the length of the puddle? The bicycle? The size of the wheels?

3. Draw a semicircle. Along its diameter draw smaller semicircles (not necessarily the same size) that touch each other. Because there are no spaces in between, the sum of the diameters of the small semicircles must equal the diameter of the large one. What about their perimeter, the sum of their arc lengths?

4. Choose any smallish number N. How can you cut a circular shape into N parts of equal area with lines of equal lengths, using only a straight-edge and compass? Hint: The lines don’t have to be straight.

[Solutions at Alexander Bogomolny’s Pi Page. Scroll down to “Extras.”]

It can be of no practical use to know that Pi is irrational, but if we can know, it surely would be intolerable not to know.

— Edward Titchmarsh

Here are a few pi-related links you may find interesting:

Or for pure silliness:

Have fun playing math with your kids!

## Playful Math Education 162: The Math Games Carnival

Welcome to the 162nd 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/activity in honor of our 162nd edition. But if you’d rather jump straight to our featured blog posts, click here to see the Table of Contents.

## Try This Puzzle/Activity

The number 162 is a palindromic product:

162 = 3 x 3 x 2 x 3 x 3
and 162 = 9 x 2 x 9

• How would you define palindromic products?
• What other numbers can you find that are palindromic products?
• What do you notice about palindromic products?
• What questions can you ask?

Make a conjecture about palindromic products. (A conjecture is a statement you think might be true.)

Make another conjecture. How many can you make? Can you think of a way to investigate whether your conjectures are true or false?

## The Colors-of-Fall Carnival: Playful Math #160

Welcome to the 160th 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/activity in honor of our 160th edition. But if you’d rather jump straight to our featured blog posts, click here to see the Table of Contents.

## Try This Puzzle/Activity

Appropriately for an October carnival, 160 is an evil number.

A number is evil if it has an even number of ones in binary form. Can you find the binary version of 160? (Hint: Exploding Dots.)

160 is also a polyiamond number. If you connect 9 equilateral triangles side-to-side, a complete set of 9-iamond shapes would have 160 pieces.

But sets that large can be overwhelming. Try playing with smaller sets of polyiamonds. Download some triangle-dot graph paper and see how many different polyiamond shapes you can make.

What do you notice? Does it make you wonder?

What designs can you create with your polyiamonds?

Photo by Daiga Ellaby on Unsplash

## 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?

Once again, the delightful Nrich Maths website offers a seasonal selection of activities to encourage your children’s (and your own!) mathematical creativity.

Click the images below to visit the corresponding December Math Calendar pages.

### For Primary Students

Here are twenty-four activities for elementary and middle school, one for each day in December during the run-up to Christmas.

When you get to the Nrich website, click a number to go to that day’s math.

### For Secondary Students

Here are twenty-four favorite activities for middle and high school, one for each day in December in the run-up to Christmas.

When you get to the Nrich website, click a number to go to that day’s math.

### More Holiday Math

I encourage you also to explore my HUGE holiday math post:

Or check out these pages for more ideas:

Have fun playing math with your kids!

CREDITS: “Peanuts Christmas Panorama” photo [top] by Kevin Dooley via Flicker. (CCBY2.0)

## “Black Friday” Shopping Season Discount

‘Tis the season for discount sales. I usually ignore the annual Black Friday push, because NOT shopping is an even better way to save money.

But this year, my publishing company Tabletop Academy Press has decided to join in the fun.

So if you’re looking for new math activities to play with your kids, I’ve just added several new books and discount bundles to our online store — including a huge variety of math journaling resources.

And for the next week or so, you can get 15% off anything in our store by using the coupon code TABLETOP15 at checkout.

Including:

But act fast! The discount code expires December 5th.

## Playful Math Journaling: Try It for Yourself

Math journaling helps students enjoy the adventure of learning math through playful exploration.

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.

All they need is a piece of paper, a pencil, and a good prompt to launch their mathematical journey.

### Give It a Try

• “Five Types of Journaling Prompts,” a short excerpt with example prompts from my new book 312 Things To Do with a Math Journal
• Four sample task cards from the accompanying series of printable Math Prompt Task Card books
• And a few pages from my Adventurous Student Journals (also known as the Math Rebel journals) to get kids writing

### Back the Kickstarter

And if you like what you see, I’d love to have your support for my Playful Math Journaling Kickstarter project. Check it out:

## Global Math Week 2021

### Exploding Dots and Much More

I can’t believe we’re getting ready for the 5th Global Math Week. Wow!

Have your kids had a chance to play with Exploding Dots? Or Pencil Pushing, or Garden Paths? Or any of the other fun projects from the creative brain of James Tanton?

Check out the Global Math website for details and links.

## 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.

## Notice, Wonder, Create

Many homeschooling parents dream of a mathematical magic bullet — a game, app, or book that will help their children learn math and enjoy it.

As in life, so also in math, there is no magic solution.

Do you want your children to learn math and enjoy it? Teach them to be Math Makers.

When they create their own math, students build deep, personal connections to math concepts. They think about the relationships between numbers, shapes, and patterns. Math becomes personal.

Toys, hobbies, favorite stories — all can be fodder for math creation.

### Where Do Math Makers Get Ideas?

Let the child choose something to think about.

Make an “I Notice” list. How does that item relate to math? What patterns or shapes can you see?

Or how would the story characters use numbers in their daily lives? Would they cook, or go shopping? Might they build something? Would they decorate it with a design? What would they count or measure?

Make an “I Wonder” list. How many different ways might you turn the things you noticed into questions? What else might you ask?

Then turn one of your noticings or wonderings into a math story, poem, puzzle, drawing, or game. Create your own math. Share your creation with family and friends.

### Now Get Published

Join the Student Math Makers team. We’d love to add your math creation to our collection and share it with viewers all around the world!