Sweet and Sour Circles

Here's your nightly math! Just 5 quick minutes of number fun for kids and parents at home. Read a cool fun fact, followed by math riddles at different levels so everyone can jump in. Your kids will love you for it.

Sweet and Sour Circles

March 14, 2016

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 the edge. So as we think about circles, it’s also a great time to celebrate some of our favorite circle-shaped foods, like oranges, lemons and limes. If you slice across any citrus fruit to see its “cross-section,” you’ll get a circle divided into little pie pieces — not pi, but pie! The sections, called “liths,” show up as little triangles. So how many sections does an orange or lemon have? Unlike pi, there’s no exact number. From photos, it looks like most lemons have 8 or 9 segments; oranges have 10 to 12; limes have up to 12, too; 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: Which has more sections, a 10-lith lime or an 8-lith lemon?

Little kids: If your orange has 12 cute little pie sections, and 4 of them have seeds you have to spit out, how many don’t?  Bonus: If you then eat 1/2 the sections with no seeds, how many do you eat?

Big kids: 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 your 2 grapefruit each have 14 dots, do you have enough sections to feed 30 people?  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: The lime.

Little kids: 8 seed-free sections.  Bonus: 4 sections.

Big kids: No, you only have 28 segments.  Bonus: 3 grapefruit and 1 lemon. If you subtract 9 from 51, the only result that is divisible by 14 is 42 (51 minus 9).

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About the Author

Laura Overdeck

Laura Overdeck

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 while still in diapers, 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.

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