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Pi Day

Pi (Greek letter “π”) is the symbol used in mathematics to represent a constant — the ratio of the circumference of a circle to its diameter — which is approximately 3.14159. It is the ratio of a circle’s circumference to its diameter. Pi is a constant number, meaning that for all circles of any size, Pi will be the same.  Want to know more about PI? Read the brief history of Pi here!

There are many ways of observing Pi Day. Here are some fun ideas for you to incorporate into your day:

  • Discuss the number π. Check out the brief history of π here and how to compute digits of pi here.
  • Complete interactive exercises at the end of this lesson plan. Here are some fun Pi Day activities.
  • You can discuss this BBC article about Pi.
  • Listen to the Pi Day Song.
  • End your Pi Day celebration by eating pie!

10 Fun Facts about Pi

  1. Pi is the number of times a circle’s diameter will fit around a circles circumference.
  2. Pi is the 16th number in the Greek alphabet. In the English alphabet, p is also the 16th letter.
  3. If one billion digits of pi were printed in average it would go from NYC to the middle of Kansas (this has been tested).
  4. Pi is also a food, but that is spelled p-i-e.
  5. Pi is the most recognized math symbol in the world.
  6. Pi is also referred to as the “circular constant,” “Archimedes’ constant,” or “Ludolph’s number.”
  7. Some scientists believe Japanese is the best language to memorize pi.
  8. Even computers can’t compute pi, so don’t feel bad if you can’t.
  9. Isaac Newton calculated pi to at least 16 decimal places.
  10. Albert Einstein was born on pi day (3/14/1879).

 Help us celebrate this never-ending number (3.14159 . . .) and Albert Einstein's birthday:


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  • Follow us on Twitter and join the conversation using the hashtag #O4K and #PiDay