Sunday, March 11, 2012

How To Use An Abacus : Addition

I told you the other day that I had figured out how to use the (rainbow) abacus.
I just never knew.  I really didn't.
And in case there is someone else out there who doesn't (and would like to know), here I am.

We've used ours often enough, that's true.  It has hung out on the computer table for years, on and off.  Mostly for JumpStart games, and the like.  (Sixteen plus seven is what?)

But this is a whole different thing.
This way one can sum up to ten billion, nine hundred ninety-nine million, nine hundred ninety-nine thousand, and nine hundred ninety-nine.  More than I've ever needed to add.  :)


Here's what I showed my children the other day.
We'll start with the simple stuff.

Let's say... 13 + 5.
We need no more than two digits for this sum, so we'll use the top two rows.
First, 13.

One goes in the 'tens' row, three go in the 'ones' row.
Plus five.
Simple!
'One' in the tens row (ten), and 'eight' in the ones row makes 18!
Tada!

*  *  *

Next comes the more complicated stuff... but when you get this one, you get the whole thing.

18 + 25.
Pretty sure that we'll still be within two digits ;), so we'll stick with two rows.
The same '18'...

Now to add 25.
Twenty...

and now five.
One, two...


(we made 'ten', so must add that ten to the 'tens' row,


and now we'll push these back to zero)


and...three, four, five.



Aah.
'Four' in the tens row, and 'three' in the ones row.
That makes 43!

One more.
129 + 76.
We'll need three rows.
129...


plus seventy (which means adding seven in the 'tens' row)...


And then one,

(we've now made ten, so we add that 'ten' to the tens row...


and then back to zero with the 'ones' row....


but we've also used all ten of the 'tens' row of beads,


so that makes a 'hundred', so add one to the hundreds row...


and then back to zero with the 'tens' row...)


and then two, three, four, five, six.


Two in the 'hundreds' row,
nothing in the 'tens' row,
and five in the 'ones' row.
129 + 76 is...

205!.  : )

Now everyone (er... namely Me) gets to be impressed with themselves because they can easily -and differently- add four billion something to three billion something.
And even something else to that!  :)

And being impressed with one's self
is a Very Fine Thing.

17 comments:

  1. Never did understand how they worked! Thanks for showing us!

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  2. Lise - Ah, so you're the other person who didn't know! ;) Glad I wrote it for you!

    :) - Really, it has bothered me for years that I didn't have a clue what to do with one!

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  3. I didn't know, either. I always thought, Huh, you can't add up all that much with these, can you? Silly me to doubt the ancient Chinese. I will blow my kids' minds with this someday. :)

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  4. Of course if you start at the bottom you can move up the rows without having to know in advance how many you'll need ;)

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  5. we have had one for years and i haven't really thought much about it. hmmm i think i have a plan for this week. :) thanks

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  6. Tequilamonky - Sure. Starting at the bottom is practical. It just felt easier to work at eye level when I was showing the babes, and had the abacus between us.
    Seemed easier to start at the top, since that's how we call the numbers. (ie, one thousand, six hundred, sixty-four.) Then we weren't beginning in the middle of the machine. (there are no placement marks, so....)

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  7. Thank you! I've forgotten how to do it))) But already it is time to teach my daughter

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  8. Great, now I can show Zander how to use ours, thanks for sharing, maybe I knew once, if I did I'd forgotten ... he's loving math games right now so timely :) x

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  9. My intense math phobia made this step-by-step instruction scary!

    Sadly, unlike all the others who've commented, I will have to re-read and try to understand it.

    Did I mention having to change my major in college because I could not pass algebra? I took it THREE times.

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  10. Thanks for this! I had no idea before now how an abacus worked.

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  11. Wow this is great!!! Thanks for doing this.

    What is even more amazing is that I used the colors of the rainbow to help with place value.

    Units red, tens orange, yellow hundreds.... you get the picture :).

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  12. ahhhhhhhhhhhhhhhhhhhhh.
    we've had one for years...
    now we can actually use it for its intended purpose.
    thanks!!

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  13. Yay, you! We do start from the bottom, too, which I think you'll like when you get used to it. Or, you know, just start wherever--not a big deal.

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  14. Thanks for showing this. I never understood it before (never looked into it either :-)

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  15. YAY! I just bought one at Ikea and had no clue how it worked--looked it up on google and here i am. thank you!

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  16. Well, thank you very much!! I can't wait to show my kids!

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  17. Glad to have come across this - thanks!

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Thanks so much for sharing your thoughts!