It’s Pi Day, 3/14, the day we celebrate a very special number. When you multiply the width of a circle by “pi” (3.14159265…), you get the distance around its edge! So today we can also celebrate our favorite circle-shaped foods, like the glowing oranges, lemons and limes in this photo. If you slice across any citrus fruit, you’ll see a circle divided into sections called “liths.” How many liths does an orange or lemon have? Turns out there’s no exact number. Most lemons have 8 or 9 segments; oranges and limes can have up to 12; and grapefruit can have 14 or even more. And you can figure out the number before cutting the fruit — read on to learn the trick!
Wee ones: How many full orange circles can you see in the picture? Count as many as you can!
Little kids: Which has more sections, a 10-lith lime or an 8-lith lemon? Bonus: If your orange has 12 cute little sections, and 4 of them have seeds you have to spit out, how many don’t?
Big kids: SECRET: If you pull that bellybutton thing off a citrus fruit and count the little white dots under it, it tells how many sections the fruit has! If each of your 2 grapefruits have 14 dots, how many liths do they have together? Bonus: If your pile of 9-segment lemons and 14-segment grapefruit has 51 sections in total, how many of each fruit must you have?
Wee ones: We count 3 big orange circles.
Little kids: The lime. Bonus: 8 seed-free sections.
Big kids: 28 liths. Bonus: 3 grapefruit and 1 lemon. If you keep subtracting 9 from 51, the only result that is divisible by 14 is 42 (51 minus 9).
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.