This Week From Bedtime Math: Digging for Dollars

You might be able to find this kind of dollar in a sand bank as you&ll discover in today&s math challenge.
By Laura Overdeck
Aug 06, 2013



This Week From Bedtime Math: Digging for Dollars

Aug 06, 2013

What is Bedtime Math? A message from Laura: Bedtime Math is a pretty simple idea: We all know we should read to our kids at night, but what about math? My husband and I have done fun, mischief-loaded math problems with our kids at night for years, and when at age 2 our third child started hollering for his own math problem, we realized we were onto something:  In a world where so many people say, "Ewww, math!" we had created a household culture where kids don't just tolerate math, they actually seek it out. Now we email parents a fun, lively math problem every day to do with their kids – and every week, we'll be posting a new problem right here on Scholastic Parents!

We don't usually name animals after money, but someone did do that with the sand dollar. A sand dollar is a flat, hard, circle-shaped sea creature that does look like an American silver dollar, except for the pretty five-pointed star design on it. The chunkier versions are called sea biscuits or sea cookies, and they're also related to sea cucumbers, so clearly someone was also hungry when naming these guys. The thing is, you can't consume a sand dollar, because it isn't like a mussel or clam where there's a soft animal inside that you can eat. With sand dollars, that hard circle is the creature!  A sand dollar eats through its mouth, which is a tiny hole in the center of its bottom side, with five very small teeth to chew food just like we do. These hard, thin, circular creatures break easily, though, so if you do find a full sand dollar on the beach, that's pretty exciting – and that feeling might be worth more than a dollar. Speaking of exciting feelings, see if your kids can solve these sand dollar-inspired math challenges today:

Wee ones: If a sand dollar has 5 teeth and you have 20 teeth, who has more teeth?

Little kids: If you find 2 sand dollars and each one has 5 teeth, how many sand dollar teeth have you found?  Bonus: A sand dollar also has a pretty 5-pointed design on its top. If you find 5 sand dollars, how many points can you count on them in total?

Big kids: Baby sand dollars, called larvae, can each split into 2 larvae when they sense danger, as a way to confuse whoever is attacking them. This is called “cloning,” which means to make a copy of oneself. If a cluster has 9 baby sand dollars that clone themselves, and then each of the new sand dollars clones itself, how many sand dollars are there now?  Bonus: Now what if all of them clone themselves again – how many baby sand dollars now?
Wee ones: You have more teeth!
Little kids: 10 sand dollar teeth.  Bonus: 25 points.
Big kids: 27 sand dollars, because only the 9 new ones clone again.  Bonus: 54 sand dollars.

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