When You’ve Run out of Toes

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.

When You’ve Run out of Toes

February 6, 2015

Long ago before we had calculators or computers, or had even invented numbers, how did people count? Well, way back when they just had to count using their fingers and toes. But of course, we have only 10 fingers and 10 toes, so that didn’t work so well past 20. So people used rocks and sticks, and about 4,000 years ago the abacus was invented. It’s a set of smooth sticks with beads that slide back and forth: the 4 beads on the bottom are each worth 1, and the 2 top beads are each worth 5. As you count 1, 2, 3 by sliding the bottom beads up, once you reach 5 you push the 4 beads back down and slide one of the 5 beads down. When you reach 10, you push all beads away on the first stick to show the “0,” then move 1 bead on the second stick to show the 1 in “10.” This video shows a man making them really, really fast — faster than we can count!

Wee ones: If each stick has 4 beads on the bottom and 2 on the top, how many does it have in total?

Little kids: To show numbers above 10, you need to slide a 1 on the second stick, then start adding beads on the first stick. How many beads do you slide to show 13?  Bonus: How about 25? (Reminder if needed: How do you show 5 on an abacus?)

Big kids: If the man in the video can swoosh up beads onto an abacus perfectly in 6 seconds, how long does it take him to fill 5 of them?  Bonus: If he actually takes 3 minutes to hammer in the sticks, 1 minute to swoosh up the beads, and 4 minutes to snap it all together, how many abaci can he finish in 1 hour?

 

 

 

Answers:
Wee ones: 6 beads.

Little kids: 4 beads: 1 bead on the second stick, and 3 of the 1-beads on the first stick.  Bonus: 3 beads in total: 2 beads on the second stick (to show 2 10s) plus just 1 of the 5-beads on the first stick.

Big kids: 30 seconds.  Bonus: 7 of them. Each takes 8 minutes and 56 is the largest multiple less than 60 minutes.

And thank you Mary Claire A. for sending us this cool video!

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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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