# As American as Apple Pi

For Pi Day (March 14, aka 3/14), we make pie, of course! Pi is called an irrational number because it cannot be expressed as a simple fraction–22/7 only comes close, but things can get pretty crazy around my house with the allegedly rational number 4–four kids that is!

Although it is usually represented as 3.14 for basic geometry calculations, Pi has an infinite string of numbers after the decimal point. Mathematicians have calculated Pi to 50 *billion* decimal places (you can see 1 million here). You can look hard to try to find a patter in the numbers, but there isn’t one.

We like to keep things simple around here, however, so we bake a finite number of mini apple pies with pre-made puff pastry dough–easy as pie!

**Ingredients**

* 2 Granny Smith Apples, chopped

* 1 sheet puff pastry

* 2 Tbsp butter

* 2 Tbsp brown sugar

* 1 tsp cinnamon

* Muffin Tin (mini or regular)

**Recipe:**

1. Make the filling by mixing butter, apples, sugar, and cinnamon in a pot on medium heat until the mixture reaches your desired firmness.

2. Using the mouth of a jar or a cup, cut circles from the puff pastry dough and place in your muffin tin.

3. Add filling.

4. Either cover with a lattice of puff pastry strips or with another round of puff pastry–you can even cut a “pi” sign in the top round.

5. Bake according to the directions on the puff pastry canister.

*This simple recipe is easily halved or doubled. Can your kids do the math?*

*The Proof is in the Pi*

While your mini pies are baking, you can prove that the circumference of a circle is the diameter multiplied by pi (C = πd).

Just take a piece of yarn or kitchen twine and wrap it around the mouth of the jar you used to cut your rounds. Snip the yarn.

Now, stretch the yarn across the mouth of the jar and mark the diameter (a straight line from one side of the rim to the other that runs through the center point) with a marker. Do this two more times, starting from your previous mark. You should see that the circumference equals three diameters plus a little more.

Try it with a few larger and smaller circles in your kitchen. How many circles can you find? We found the tops of an oatmeal tin and a coffee tin, lots of bowls, an extra apple, and our kitchen table!

By now, your Pi Pies should be ready. Enjoy the yummy, gooey, math!

Oh, and it is Albert Einstein’s birthday, too. We would have baked him a cake but pie seems more appropriate!

***Stay tuned for details for our Bedtime Math Pi Day Twitter party at 9 PM EST on March, 14, 2014!*

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