## Math Teachers at Play #84 via Math Hombre

Rectangles, fractions, prime factorization, dancing, puzzles, great books, and so much more — check out all the fun at the March Math education blog carnival:

But Before You Go…

I’m running out of carnival hosts! Would you like to volunteer? It’s a bit of work, but great fun, too. Leave a comment here, or send me an email.

Excerpt:

Welcome to the 84th Math Teachers at Play Blog Carnival!

84 is a portentous number. It’s the sum of twin primes (What’s the previous sum of twin primes? Next?). It’s thrice perfect, twice everything. It’s positively Orwellian. It’s even a town in Pennsylvania.

84 puzzler 1:
Number the intersections of these five circles with the integers 1 to 20 so that the points on each circle sum to the same.

It was a good month for math reading related posts …

## Happy Birthday, General Relativity

Don’t forget that Pi Day is also Albert Einstein’s birthday! And this year marks the 100th anniversary of his Theory of General Relativity. So Science Magazine has a special Einstein issue online, featuring this interactive comic:

## Pi: Who Needs That Many Digits?

From Numberphile: Pi is famously calculated to trillions of digits – but Dr. James Grime says 39 is enough.

#### How you round it off makes a difference:

An extra note from Dr. Grime: “Since pi39 ends in 0, you may think we could use pi38 instead, which has even fewer digits. Unfortunately, the rounding errors of pi38 are ten times larger than the rounding errors of pi39 — more than a hydrogen atom. So that extra decimal place makes a difference, even if it’s 0.”

## Pi and Buffon’s Matches

From Numberphile: Dr Tony Padilla’s unique (and low budget) twist on the Buffon’s Needle experiment to learn the true value of Pi.

#### For a kid-friendly version of this experiment, try throwing food:

Do you have a favorite family activity for celebrating Pi Day? I’d love to hear it!

## Unending Digits… Why Not Keep It Simple?

Unending digits …
Why not keep it simple, like
Twenty-two sevenths?

—Luke Anderson

#### Math Poetry Activity

Encourage your students to make their own Pi Day haiku with these tips from Mr. L’s Math:

And remember, Pi Day is also Albert Einstein’s birthday! Check out this series of short videos about his life and work: Happy Birthday, Einstein.

CREDITS: Today’s quote is from Luke Anderson, via TeachPi.org. Background photo courtesy of Robert Couse-Baker (CC BY 2.0) via Flickr.

## Pi Day: It’s an Irrational Holiday

I just discovered this fun Pi Day song from The Singing Nerd. Definitely need to add him to my YouTube subscriptions.

Hat tip: Singing Banana.

Want to help your kids learn math? Claim your free 24-page problem-solving booklet, and you’ll be among the first to hear about new books, revisions, and sales or other promotions.

## Pi Makes a River Bend

From Numberphile: “Sinuosity is a measure of how ‘bendy’ a river is. It is the length of the river divided by the direct route. Featuring Dr. James Grime.”

### Update

After posting this video, Dr. Grimes and Lawrence Roberts began collecting and analyzing data about real-world rivers. It turns out the pi theory of sinuosity is too simple. Read about their results:

## Calculating Pi with Real Pies

From Numberphile: “How accurately can we calculate Pi using hundreds of REAL pies? This video features Matt Parker, who believes this is the world’s most accurate pie-based Pi calculation.”

Pi Day is coming soon. Maybe you’d like to try a pi project with your family? Check out my Pi Day Roundup of links.