Do you know how many teeth you have right now? As a kid your tooth-count changes all the time, since you’re losing teeth and growing new ones. So our friend Isha I. asked, how many teeth are there in the world? Well, of the 8 billion people out there, about 7 billion have their final 28 teeth, or 32 if their wisdom teeth came in. If it’s 30 on average, that gives us 210 billion teeth. If we guess that the 1 billion kids still growing teeth average 10 each, that gives us another 10 billion. But what about all our toothy animal friends? Mammals like dogs, cats, beavers and raccoons all have teeth. So do a lot of fish: sharks have 50-100 teeth at any time. It’s safe to say there are at least trillions of teeth out there – and probably not enough toothbrushes for them all!

*Wee ones:* Look in a mirror. How many teeth can you see? Count as many as you can!

*Little kids:* If you have 4 teeth on top and 4 teeth on the bottom facing them, how many teeth do you have? *Bonus:* If you then lose 2 teeth, grow 3 more teeth, lose another tooth, and then grow 2 more, how many teeth do you have now?

*Big kids:* If there are 210 billion grown-up teeth out there and 10 billion kid teeth, how many teeth is that? *Bonus:* If you start with 2 teeth and end up with 32 teeth, how many times does your number of teeth double?

*The sky’s the limit:* If at a party every kid has 10 teeth and every grown-up has 28, how many of each must you have if there are 114 teeth in the room?

Answers:

*Wee ones:* Different for everyone…see how many you can count!

*Little kids:* 8 teeth. *Bonus:* 10 teeth.

*Big kids:* 220 billion teeth. *Bonus:* 4 times: to 4 teeth, then 8, then 16, then 32.

*The sky’s the limit:* 3 kids and 3 grown-ups. Since the numbers ends in 4, and since kid teeth don’t affect the last digit (we keep adding 10), we need 3 grown-ups to give us 84 grown-up teeth. Then we need 3 more kids to add the 30 to get us to 114.

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.