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.)
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!