# How hard is it to learn air-abacus?
**URL:** https://boards.straightdope.com/t/how-hard-is-it-to-learn-air-abacus/661495
**Category:** Factual Questions
**Created:** [June 20, 2013, 7:06pm UTC](https://boards.straightdope.com/t/how-hard-is-it-to-learn-air-abacus/661495 "2013-06-20T19:06:36Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@rogerbox](https://boards.straightdope.com/u/rogerbox)
#### Post date: [June 20, 2013, 7:06pm UTC](https://boards.straightdope.com/t/how-hard-is-it-to-learn-air-abacus/661495/1 "2013-06-20T19:06:36Z")
My Japanese teacher in high school was an abacus-champion as a kid, and she demonstrated doing amazing calculations of multi-digit numbers using her fingers, simulating mentally using an abacus. I’d really like to learn to do this because I think it’d be an awesome party trick, but I don’t even know how to use an abacus yet, so I could very well be considering wasting time doing something only very gifted people could do, or something that would take years that I don’t want to invest to doing this.
I’m fairly good at mental calculations (I can multiply 2 digit numbers by 2 digit numbers pretty easily and 3 digit numbers by 3 digit numbers but it takes me a long time), would learning to do this be something I could do in a matter of months, years, decades, or possibly never no matter how hard I try?
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### Author:  [@rhysf](https://boards.straightdope.com/u/rhysf)
#### Post date: [June 21, 2013, 1:58am UTC](https://boards.straightdope.com/t/how-hard-is-it-to-learn-air-abacus/661495/2 "2013-06-21T01:58:01Z")
[This](http://boards.straightdope.com/sdmb/showthread.php?t=572370) thread may or may not be of use to you.
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### Author:  [@Senegoid](https://boards.straightdope.com/u/Senegoid)
#### Post date: [June 21, 2013, 2:14am UTC](https://boards.straightdope.com/t/how-hard-is-it-to-learn-air-abacus/661495/3 "2013-06-21T02:14:42Z")
Is there some trick to multiplying two two-digit numbers in your head, or is it just a matter of practicing a lot?
I can multiply any two-digit number by _itself_ in my head, but there’s a trick to it, and I still don’t have the practice to do it rapidly.
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### Author:  [@Monty](https://boards.straightdope.com/u/Monty)
#### Post date: [June 21, 2013, 2:57am UTC](https://boards.straightdope.com/t/how-hard-is-it-to-learn-air-abacus/661495/4 "2013-06-21T02:57:42Z")
OP: Perhaps [this Weird Earl](http://cs.iupui.edu/~aharris/chis/chis.html) entry may help you get started.
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### Author:  [@rogerbox](https://boards.straightdope.com/u/rogerbox)
#### Post date: [June 21, 2013, 6:06am UTC](https://boards.straightdope.com/t/how-hard-is-it-to-learn-air-abacus/661495/5 "2013-06-21T06:06:14Z")
> [@Senegoid](#):
>
> Is there some trick to multiplying two two-digit numbers in your head, or is it just a matter of practicing a lot?
When I was a kid I was just very bored in class so I practiced a lot. The way you would do it on paper by going right to left was how I did it so for ex:
## 64 x27
## 448 +1280
1828
The only hard part is remembering the first number, 448, while you are multiplying the second number, but once you have 1280 and remember your first number 448, it’s a simple addition problem. I’m sure there are better ways but it’s mainly a difficulty in memory and not calculation (I am actually terrible at math :smack: )
> [@](#):
>
> I can multiply any two-digit number by _itself_ in my head, but there’s a trick to it, and I still don’t have the practice to do it rapidly.
What’s the trick?
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### Author:  [@rogerbox](https://boards.straightdope.com/u/rogerbox)
#### Post date: [June 21, 2013, 6:07am UTC](https://boards.straightdope.com/t/how-hard-is-it-to-learn-air-abacus/661495/6 "2013-06-21T06:07:24Z")
> [@Monty](#):
>
> OP: Perhaps [this Weird Earl](http://cs.iupui.edu/~aharris/chis/chis.html) entry may help you get started.
That is really cool! I will start on that since it won’t take me learning how to do an abacus, but I think I still want to learn air-abacus, because it’s so cyberpunkish looking. 😉
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### Author:  [@Senegoid](https://boards.straightdope.com/u/Senegoid)
#### Post date: [June 21, 2013, 6:46am UTC](https://boards.straightdope.com/t/how-hard-is-it-to-learn-air-abacus/661495/7 "2013-06-21T06:46:00Z")
> [@rogerbox](#):
>
> > [@Senegoid](#):
> >
> > I can multiply any two-digit number by _itself_ in my head, but there’s a trick to it, and I still don’t have the practice to do it rapidly.
>
> What’s the trick?
If you can already multiply any two 2-digit numbers fairly fluently, then I don’t think you would gain much by learning a special “trick” for squaring any 2-digit number.
Anyway, here it is. The algebra makes it look even uglier, but it happens that the arithmetic works out easier in your head.
Consider any 2-digit number AB (where A and B are the individual digits). The actual value, of course, is (10A + B). Squaring this gives:
(10A + B)[sup]2[/sup] = 100A[sup]2[/sup] + 20A\*B + B[sup]2[/sup]
This may look ugly, but it’s actually easier to work in your head.
Example: 74[sup]2[/sup] = 4900 + 560 + 16 = 5476.
(For the middle term, think: 7\*4=28, \*2=56, \*10=560.)
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### Author:  [@rogerbox](https://boards.straightdope.com/u/rogerbox)
#### Post date: [June 21, 2013, 7:00am UTC](https://boards.straightdope.com/t/how-hard-is-it-to-learn-air-abacus/661495/8 "2013-06-21T07:00:50Z")
I will check that out tomorrow when I’m not so tired and give it a whirl. I can multiply two digit numbers but it takes me a while, in fact I should time myself tomorrow to see how fast I can do, I’m curious.