Geometry Middle School

Happy Summer Pi Day!

Math teachers love March 14, the day where we have a built-in excuse to strong-arm students into bringing cookies, cakes, and pies to class, all under the clever guise of celebrating our irrational friend.  But while we celebrate and embrace 3.14, its fractional buddy 22/7 often trudges on without fanfare.  So, on this July 22, consider this challenge:

  • Which approximation of pi,  3.14 or 22/7, is better?

What spirited debates which can take place by assigning students a side to defend?  A quick visual inspection of the protagonists, labeled on a number line, provides some initial evidence:

Number Line 1

Additionally, this is a great time to discuss and compute error.  Just how far away are we from what we would like to estimate?  And how good of a job have we done?

Number Line 2

Evelyn Lamb provides some pi anecdotes in this month’s Scientific American.  How many digits of Pi does NASA utilize in calculations?  Why do people seek to memorize the digits of pi?

So raise a glass to the “real” pi day!  Off to seek some fresh blueberry pie……


By Bob Lochel

HS Math Teacher. Hatboro-Horsham School District, Horsham, PA.

One reply on “Happy Summer Pi Day!”

Despite the fact that 22/7 is my birthday, it took me several years of teaching math before I ran across a reference to it as an approximation of pi. (bonus fact – also “rat catcher’s day!” )

Since the reason to use March or July largely stems from the difference in date format (d/m/y vs m/d/y ) I spent several years referring to 22/7 as Quince, mincemeat or European Pi Day. That worked mainly because quince is just an awesome, funny word.

I converted to tau last year, and while June 28th is closer to the school year, it’s nowhere as useful as Pi Day, which breaks up the March doldroms. That said, asking MS kids to choose and argue for one particular circle holiday was a remarkable entertaining hour.

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