Today is Pi Day, and do you know why? If you cut a string that is the width of a circle, like a bike tire, you’ll need a little more than 3 of that string to wrap all the way around the edge. The exact number comes to 3.14159265…(it goes on and on). March 14, when written as 3/14, looks like the start of that number, so we have Pi Day. We use pi every day. As our friend Mary Claire A. shared, if you wrap a measuring tape around your head, find that length in inches, and divide by pi, you’ll get the width of your head — and that is your hat size! Better yet, when you bake a pie, the width tells you how much crust you’ll need around the edge…and that is the best pi of all.

*Wee ones:* Try to find 3 circles in your room.

*Little kids:* If you slice one pie into 6 slices and another same-size pie into 4 slices, which pie has bigger slices? Bonus: How many slices do the 2 pies have in total?

*Big kids:* If your bike has 2-foot-wide tires and they turn 10 times as you ride, about how many feet did you roll? (You can round pi to 3 if you like, or use 3 1/7, or try 3.14!). Bonus: If your head is 22 inches around, what hat size do you wear?

*The sky’s the limit:* If you ride 440 feet, how many times did the 2-foot-wide wheels turn, if you round pi to 3 1/7?

Answers:

*Wee ones*: Answers might include clocks, edges of plates and cups, and Frisbees.

*Little kids:* The slices from the 4-slice pie are bigger: you cut fewer slices, so each has more pie in it. Bonus: 10 slices.

*Big kids:* The tire is about 6 feet around (or 6 1/7, or 6.28), so you ride about 60 feet (or 60 +20/7, which equals 62 6/7…or 62.8). Bonus: About size 7.

*The sky’s the limit:* 70 times. 2 x 3 1/7 (or 22/7) is 44/7, and if 440 is 44/7 of the wheel turn count, then 440 divided by 44 gives you 1/7 of it. 440/44 is 10. So 10 is 1/7 of the total turn count, giving us 70 turns.

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Laura Bilodeau Overdeck is founder and president of Bedtime Math Foundation. Her goal is to make math as playful for kids as it was for her when she was a child. Her mom had Laura baking before she could walk, and her dad had her using power tools at a very unsafe age, measuring lengths, widths and angles in the process. Armed with this early love of numbers, Laura went on to get a BA in astrophysics from Princeton University, and an MBA from the Wharton School of Business; she continues to star-gaze today. Laura’s other interests include her three lively children, chocolate, extreme vehicles, and Lego Mindstorms.