A World of Legs

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.

A World of Legs

December 2, 2015

Spiders aren’t always the prettiest animals. But most spiders are our friends, since they eat bugs that we don’t like. This led Bedtime Math fan Charlie Y. to ask, how many spiders are in the whole world? (along with her awesome picture of a spider!) Well, we’ve heard that no matter where you are, there’s always a spider within 3 feet of you. Is that true? Sure enough, spider-counting scientists have tried to figure this out. For just one type, the wolf spider, they found about 1 for every square meter of ice in the Arctic, and 3 of them for every square that size in Europe (a meter is a little more than 3 feet). Another bunch of people then added this up for all 40,000 types, or “species.” There are more of some kinds than others, and they came up with about 130 spiders per square. This comes to 130 million in every square kilometer (a little more than 1/2 mile), and for all of Earth’s 149 million square km, we get 19 quadrillion spiders.  If you think that’s a huge number, try counting up their legs!

Wee ones: A spider has 8 legs.  Can you count from 1 to 8?

Little kids: If you have a pet spider, how many legs do the two of you have together?  Bonus: How many more legs than you does your spider have?

Big kids: If you walk 20 feet and pass a spider every 2 feet – including right where you started – how many spiders do you see?  Bonus: If there are 20 million spiders in your state, how many legs do they have?

 

 

 

Answers:
Wee ones: 1, 2, 3, 4, 5, 6, 7, 8.

Little kids: 10 legs.  Bonus: 6 more legs.

Big kids: 11 spiders, since you see one before each of the 10 2-foot chunks, plus 1 more at the end.  Bonus: 160 million fuzzy legs.

And thank you again Charlie for the question and the cool drawing!

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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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