 Previous Messages |
Posted By
Lavina
on 2007-01-11
05:15:18
 |  Re: LOL maths
Last night I remembered, that several years ago (7-8) I began to wonder about this again. Then, I made an equasion to find out why this worked. So I made something like this:
10x+y-(x+10y)=9x-9y=9(x-y) where abs(x-y) ={1->9} So actually the result of the original substraction is the simple multiplication table of 9...  I also found out in primary school, that this multiplication table of 9 (when multiplying 9 with an 1 digit number) works like this: 9*x = ZQ where the two digits of the result are Z and Q; Z=x-1 and q=10-x / So in decimal the result is 10*(x-1)+10-x=9*x /
So I got stuck at this point 7-8 years ago. Sadly, they did not mention this phenomena on accounting seminars at the uni.
Cheers Mike! 
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Posted By
Lavina
on 2007-01-10
04:04:22
| Re: LOL maths
well, I discovered this at an age of around 10-11. Btw, I hate accounting...
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Posted By
SVS
on 2007-01-10
02:38:41
 | Re: LOL maths
That is "The Sum of Nines", an accounting trick to determine if a number has been transposed during keyboard/adding machine entry.
Where's SVS? He should know about this also....
ehehe I'me here. You are right. It happens that, at my work as accountant, I have sometimes to search for a balance error, a value multiple of 9 (for example 9, 27, 81). In all this cases a number was transposed! This helps me to guess the wrong value to be searched for.
(For example an error value o 27 can be generated by a 63 instead of 36)
A good feature of this mode is that there is only one occurrence every ten. (The same example of 27 is possible for 63-36 74-47 85-58 etc.).
Waiting for Litwr (math genius) post!!!
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Posted By
JamesC
on 2007-01-09
23:38:40
| Re: LOL maths
If you substract a two digit number XY from its reverse order 2 digit number YX, the absolute value of the result will be either one digit; always 9, (if x and y are not equal, of course), or two digits; the result's two digits Z and Q will follow this rule: Z+Q=9
That is "The Sum of Nines", an accounting trick to determine if a number has been transposed during keyboard/adding machine entry.
Where's SVS? He should know about this also....
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Posted By
indi
on 2007-01-09
16:30:36
| Re: LOL maths
Man...I thought I was sad and had no life!!!
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Posted By
Pepax
on 2007-01-09
15:00:18
| Re: LOL maths
Looks like not only C= fans entertain themselves this way....
link
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Posted By
Lavina
on 2007-01-09
08:41:18
| Re: LOL maths
... lessons were boring.
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Posted By
indi
on 2007-01-09
08:21:28
| Re: LOL maths
hehehe...you have no friends do you?
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Posted By
Lavina
on 2007-01-09
07:59:51
| Re: LOL maths
In my childhood I also entertained myself finding such special occurances in maths...
For example I realized the following:
If you substract a two digit number XY from its reverse order 2 digit number YX, the absolute value of the result will be either one digit; always 9, (if x and y are not equal, of course), or two digits; the result's two digits Z and Q will follow this rule: Z+Q=9
54-45 = 9
96-69 = 27 (2+7=9)
59-95 = -36 (3+6=9)
I made some pretty nice magic tricks with this back in primary school. I presume there are plenty of such things in maths.
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Posted By
Bionic
on 2007-01-08
15:52:16
| Re: LOL maths
Well, they know why they did not use f.e. 89x78 as an example
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Posted By
Bionic
on 2007-01-08
15:50:39
| Re: LOL maths
Think about it. It is exactly the same way you learned it in school.. Counting the intersection is actually the same as multiplying the individual digits of each other number. And then you just have to add them without messing up. It works, is just slightly more confusing
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Posted By
indi
on 2007-01-08
15:09:46
| Re: LOL maths
lol....Looks to me like a con..They just pick a couple of numbers that look like working!
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Posted By
Ulysses777
on 2007-01-08
11:28:18
| Re: LOL maths
Looks like a fancy way of doing long multiplication
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Posted By
Sidius
on 2007-01-08
08:29:39
 | Re: LOL maths
>I wonder why is it working at all?
Indeed, I am no arithmetic genius, but I introduce it to me not really...
Maybe we should ask there once Plus4Vampyre...he is, in the end, a certificate mathematician!
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Posted By
Rachy
on 2007-01-08
05:05:34
| Re: LOL maths
Hm, interesting way of multiplying. I wonder why is it working at all?
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Posted By
Lavina
on 2007-01-08
02:45:16
| LOL maths
http://www.glumbert.com/media/multiply
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