For Your Rock Collection…

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.

For Your Rock Collection…

September 16, 2015

Today is Collect Rocks Day, a great excuse to dig up dirty rocks and save your favorites. One fancy kind of rock is a “fossil,” a piece of a long-ago animal or plant that has hardened into rocks over thousands of years. And, as Bedtime Math fan Gavin A. has shared with us, scientists have found some very exciting old bones in South Africa. They’re human bones from a very, very long time ago, found in a dark cave with just a 7-inch hole to enter it. The hole was so small that the 6 scientists who crawled in to get the bones all had to be women! They’ve been called “underground astronauts” for doing this most dangerous dig. In the 2 years since the cave was found, the team has already pulled out more than 1,500 pieces from at least 15 different people. They belong to a whole new type, or “species,” of human that we’d never found before, Homo naledi. Hopefully the next batch of bones will show up in an easier place to reach.

Wee ones: Which is smaller, a 7-inch hole or a 9-inch hole?

Little kids: If you’re small enough to fit through that hole and join the 6 “underground astronauts” in the dig, what number underground astronaut are you?  Bonus: If they found this cave 2 years ago, in what year did they start digging up these bones? (We’re in 2015 now.)

Big kids: If you dig up a bone, then a worm, then a regular rock, then start over with a bone, a worm, a rock …which number item is your 6th worm?  Bonus: If they’ve found about 1,500 pieces of bone that they think belong to 15 people, about how many bones are there from each person if they’re divided up evenly?




Wee ones: The 7-inch hole.

Little kids: The 7th.  Bonus: In 2013.

Big kids: Your 17th item. You dig it up after you’ve done 5 full sets (items 1 through 15) plus your next bone (#16).  Bonus: About 100 apiece.

And thank you again Gavin for telling us about this amazing discovery! For all our fans out there, if you have an idea for a great math problem, email us at to tell us.  If we haven’t written about it before, we’ll turn it into a daily math post and give you a shout-out!

Print Friendly, PDF & Email

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 before she could walk, 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.

More posts from this author