### Every circle is a Pi but not every pie is a circle.

**MATHEMATICS** Each year March 14 is a U.S. annual celebration of **Pi Day**. But this year **Pi Day** is on a Friday, which happens to rhyme (if that makes it any easier to remember). Math geeks will engorge themselves with pie while having discussions about — you guessed it — **Pi**, which will no doubt include plans for 2015. Next year **Pi Day** will be a once-in-a-century event on 3/14/15; 9:26:53, where the U.S. m/d/y formatted date corresponds to as many as 10 digits of **Pi** (3.141592653). Even Albert Einstein was born on **Pi Day**. So you're among some great minds as you contemplate the date.

#### What Goes Around Comes Around

**Pi** (π) is the 16th letter of the Greek alphabet that is used to represent the numeric constant associated with the circumference of a circle. Whew! Take any circle, regardless of size, and divide the circumference by the diameter (distance across center) and you will end up with **Pi**. Conversely, you can multiply the diameter by **Pi** to find out the circumference, which is probably more useful. To find out how many steps it takes to walk around a perfectly round track, walk straight across the middle. Then multiply your steps times **Pi**. You can also approximate how long it takes to walk the track by multiplying the duration you walked straight across by **Pi**.

**Pi** is an irrational number (which sounds contradictory to a constant). This means it has decimals that neither end or repeat patterns. Computers have calculated more than the first six billion digits of **Pi**. Since your calculator's display area is limited, you can view 10,000 digits on CNN.

Want more **Pi Day** madness? To find out the perimeter of a square, simply multiply the length of a side by 4. If you center an overlapping a circle of equal width, there is how much space in each corner? Subtracting **Pi** from 4 equals 0.86. Divide this by 4 to reveal that each of those semi-triangles is 0.215 percent of the square perimeter. If you bake a square cake that is 9.132 inches wide (w) and you cut it into a perfect circle with an equal diameter, you will have wasted 10 **Pi**'s (w*4*0.86). Multiply by the cake thickness for volume.

#### Pi in the Face

If you're not inspired to bake a pie, here's a Kraft recipe you can prepare in 10 minutes with no baking. It would take more effort to drive to a local bakery (if you remembered to order in advance). Regardless of your sweet tooth or absence thereof, you can strive to memorize at least the first 10 decimal digits of **Pi**. This will keep you from staring like a deer in the headlights at the water cooler. It also allows you to say something other than "Nerd!" when someone mentions **Pi Day**. And we *know* the weekend talk will be, "What did you do for **Pi Day**?"

Since next year is a centurial event, we already found out the first four digits right of the decimal point: 3.**14****15**. Recall the next three digits as a set; the "9" is transposed "2" a "6." This brings us to 3.**1415****926**. Conclude with "5-35." So **Pi** with ten digits is 3.**1415926****535**. For extra credit, add the last two digits for "8," which is often rounded up to "9" since the following three digits are "979." Wow, you're already up to 14 digits: 3.**1415926535****8979**…

#### Make Pi Day Special

Congratulations! When you go out for Greek dinner with three other friends this evening, divide the check by **Pi** after reciting its successive decimals around the table. Since there's 3+1 of you, three pay 3.14 percent. Let the designated driver pay the remaining 0.58 percent. (You *are* driving, right? Plan ahead while sounding spontaneous.) For more of a challenge, let the person who can't name the next digit pay the tab.

As a reward for your effort, Store.ClinicalPosters.com has a **Pi Day** special. Get 3.14 percent off your order when you purchase at least 3 posters plus one frame (minimum cost $91.06) on March 14. ~~Use promo code 3.1415926535 to redeem your discount during checkout.~~ If you spend exactly $100 your savings equals **Pi**.

Don't need anatomy posters? The National Council of Teachers of Mathematics has a page with numerous activities and resources. What are your plans for 2015 **Pi Day**?