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.

December 3, 2015

Have you ever seen an old-fashioned clock with letters on it instead of numbers? We bet it had a bunch of Is, Vs and Xs, right? Those are Roman numerals from long ago. They used the letter I to mean the number 1; V for 5, because it was shaped like your hand making a V (5 fingers); and X for 10, made by crossing 2 hands (10 fingers total). For numbers 1 less than a major number, they put the I before that letter. So IV = 4, and IX = 9. So this became messy as numbers got bigger. Well, in a link shared by our friend Talie B., a guy called the Human Calculator tells us how each Arabic numeral can be drawn to have its own number of angles, to make them easy to remember. So a 1 has 1 angle, a 2 (which looked like a Z) has, you guessed it, 2 angles, and so on. You have to draw a really crazy 9 to get 9 angles! But it still works, and now those Roman numerals show up only to count hours and Super Bowls.

*Wee ones:* Which number from 1 to 9 is your favorite – and is it more than, less than, or the same as your age?

*Little kids:* In the number 4162, which digit is biggest? *Bonus:* How many angles do they have all together?

*Big kids:* If you drew a crazy new number with 17 angles, what pairs of numbers could you add to it to get 23? (Don’t worry about the order — just which go with which.) *Bonus:* Try to guess the mystery number…If you double it, add 5, and double it again, you get 42. What is the number?

*The sky’s the limit:* If you’re choosing 2 numbers from 1 to 9, how many ways can you pick 2 odd numbers? (Again, don’t worry about the order – but you can’t pick the same digit twice.)

Answers:

*Wee ones:* Different for everyone…pick your favorite number, and see if you have to go up or down from your age to get there.

*Little kids:* The 6. *Bonus:* 13, since they add up to 13.

*Big kids:* 3 choices. The pairs just need to add to 6, so they can be 1 and 5, 2 and 4, or 3 and 3. *Bonus:* 8. You had 21 before doubling, you had 16 before adding 5…so you had 8 before doubling that first time.

*The sky’s the limit:* There are just 5 odd digits – 1, 3, 5, 7 and 9 – and as you pair each one with other numbers, you cut down the number of pairs left to do with those. So you have 1-3, 1-5, 1-7 and 1-9 (4 choices), then 3-5, 3-7 and 3-9 (just those 3 choices, because you already did 3-1). That leaves 5-7, 5-9 (2 more), and finally 7-9, giving us 4+3+2+1=10.

Thank you again, Talie — and those of you who want to add and multiply really, really fast to wow your friends, watch the video to see how Scott Flansburg the Human Calculator does it!

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 while still in diapers, 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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