# This Week From Bedtime Math: Don't Cave In

There&s more to the ground than just dirt. The fun adds up as we go underground in today&s Bedtime Math challenge.
By Laura Overdeck
Aug 27, 2013

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Aug 27, 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!

Caves might be dark, damp, and full of squeaky bats flying around, but really, they're a great place to hang out. Caves are one of nature's most fascinating sites to see. As water seeps down from the ground above, it picks up minerals called calcites. Then, as it drips from the roof of the cave, the water leaves behind the calcite, which grows like candle wax into long spikes called stalactites. The drops that drip to the ground underneath the stalactite pile up calcite down there too, creating upward-growing spikes called stalagmites. One way to remember which is which: "stalactite" has a "c" for ceiling, while stalagmite has a "g" for "ground"…also, stalactites hang on "tight" to keep from falling. You don't want to try to watch them grow: they grow way more slowly than the hair on your head, which is pretty slow as it is. If you visit a cave, hopefully you'll find formations already there.

Now, see if your kids can "form" the answers to these cave-inspired math challenges.

Wee ones: If you step into a cave that has 3 stalactites and 3 matching stalagmites below them, how many spikes do you see in total?

Little kids: As a stalactite droops and its stalagmite grows upward, they can eventually meet to form a column. If each one has grown 15 feet when they meet, how tall is the column?  Bonus: How much had each one grown when they still had 2 feet of space between them?

Big kids: Most stalactites grow about 1/200th of an inch a year. How long will it take one to grow half an inch?  Bonus: Human hair grows way faster, about half an inch per month. How long would your hair grow if you skipped haircuts for that same stretch of time?

Wee ones: 6 spikes in total.

Little kids: 30 feet.  Bonus: Each one has 1 more foot to go, so each has grown 14 feet.

Big kids: 100 years.  Bonus: That's 1,200 months, so 600 inches – which is 50 feet of hair!

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