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#1
Old 06-20-2013, 03:06 PM
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How hard is it to learn air-abacus?

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?
#2
Old 06-20-2013, 09:58 PM
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#3
Old 06-20-2013, 10:14 PM
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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.
#4
Old 06-20-2013, 10:57 PM
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OP: Perhaps this Weird Earl entry may help you get started.
#5
Old 06-21-2013, 02:06 AM
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Quote:
Originally Posted by Senegoid View Post
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 )


Quote:
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?
#6
Old 06-21-2013, 02:07 AM
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Originally Posted by Monty View Post
OP: Perhaps this Weird Earl 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.
#7
Old 06-21-2013, 02:46 AM
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Originally Posted by rogerbox View Post
Quote:
Originally Posted by Senegoid View Post
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)2 = 100A2 + 20A*B + B2

This may look ugly, but it's actually easier to work in your head.

Example: 742 = 4900 + 560 + 16 = 5476.
(For the middle term, think: 7*4=28, *2=56, *10=560.)
#8
Old 06-21-2013, 03:00 AM
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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.
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