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.


August 17, 2014

We love learning new words here at Bedtime Math, and we just discovered a great one, “porcupette“:” it’s a baby porcupine. As cuddly as porcupines look, we also know they’re extremely prickly: a porcupine can have up to 30,000 quills! And those quills can be up to 5 inches long. Luckily porcupines can’t actively shoot their quills at you, but if you scare a porcupine while touching it, it will let them loose and their points will stick into your hand. The porcupine is the 3rd-largest rodent, after the capybara and beaver, and it isn’t the fastest-moving animal, but when scared they can break into a gallop. Some weigh as much as 60 pounds, but other types are as small as 2 pounds, making it a very huggable, holdable pet – if you’re sure it won’t prickle you with its quills.

Wee ones: If porcupines are the 3rd largest rodent, how many rodents are bigger than they are?

Little kids: If a family of 2 porcupines and their 5 baby porcupettes wanders into your yard, how many prickly animals is that?  Bonus: If you wanted to see a dozen prickly animals total, how many more porcupettes would have to show up?

Big kids: Who weighs more, you or a 60-pound porcupine – and by how much?  Bonus: A human head has about 100,000 hairs on it. How many more hairs do you have than a porcupine’s 30,000 quills?

The sky’s the limit: If you’re picking pets from some 40-animal mix of porcupines and porcupettes, and you choose 1/4 of the porcupines and 1/6 of the porcupettes, how many of each do you have if you end up with 7 animals?




Wee ones: 2 other rodents.

Little kids: 7 animals.  Bonus: 5 more porcupettes.

Big kids: Different for everyone…subtract your weight in pounds from 60, or subtract 60 from your weight.  Bonus: 70,000 more.

The sky’s the limit: You’ll end up with 1 porcupine and 6 porcupettes. If we call the two sizes P and p, we know:

P + p = 40
1/4P + 1/6p = 7

Substituting, we get
1/4 x (40 – p) + 1/6p = 7
so 10 – 1/4p +1/6p = 7

Subtracting terms from both sides, you can flip it around to get
10 – 7 = 3 = 1/4p – 1/6p

Multiply through by 12 to simplify…
36 = 3p – 2p = p

So there are 36 porcupettes, and therefore 4 porcupines. You choose 1/6 of the little guys and 1/4 of the big guys, giving you 1 porcupine and 6 porcupettes.

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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 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.

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