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#26 2006-12-20 18:39:40

John E. Franklin
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Registered: 2005-08-29
Posts: 3,582

Re: Cool Subtraction For Kids

Devante, could you do a few more examples.
Don't even try to explain, but a bunch of numbers would be helpful.
Your method looks quite interesting, and obviously fast.


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#27 2006-12-20 18:54:41

Devantè
Real Member
Registered: 2006-07-14
Posts: 6,400

Re: Cool Subtraction For Kids

Example 1;

1098-772

(772+300)+26

1098-772 = 326

---

Example 2;

5897-2653

(+3000)+200+44

= 3244

Example 3:

2097152-524288

(+1500000)+(73000)-136

= 1572864

The 136 was subtracted from my answer because I went over.

Last edited by Devanté (2006-12-21 19:05:25)

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#28 2006-12-21 11:45:33

John E. Franklin
Member
Registered: 2005-08-29
Posts: 3,582

Re: Cool Subtraction For Kids

Super examples!!  I like it!!
One typo in answer of #3, perhaps edit it.
Thanks for the lesson smile


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#29 2006-12-21 19:06:27

Devantè
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Registered: 2006-07-14
Posts: 6,400

Re: Cool Subtraction For Kids

Ah, I see I made such stupid typo. :\

Hope you like the method. smile

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#30 2006-12-21 19:35:11

luca-deltodesco
Member
Registered: 2006-05-05
Posts: 1,470

Re: Cool Subtraction For Kids

Devanté wrote:

12345-6789

= (+6000)-444
= 5556

Using my method this would only take a second or two...

youre method is the way i usually would do these sort of things in my head, but when its something thats not so easy i would have to write it down on paper, im not too good with mental arithmetic


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#31 2006-12-21 19:54:23

Devantè
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Registered: 2006-07-14
Posts: 6,400

Re: Cool Subtraction For Kids

OK.

Reaction Math would probably improve your mental arithmetic skills, then. smile

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#32 2010-11-24 08:54:03

John E. Franklin
Member
Registered: 2005-08-29
Posts: 3,582

Re: Cool Subtraction For Kids

4 years has passed since luca posted the post # 4 of this thread, and
it was funny because I had forgotten he taught me that, so this morning
I redeveloped the same method with the increment on the bottom for the
carry, and showed it to my mom.  She thinks I came up with it, but really
it was luca-d that did!!!!


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#33 2010-12-04 04:16:44

John E. Franklin
Member
Registered: 2005-08-29
Posts: 3,582

Re: Cool Subtraction For Kids

I played around with luca-d's method for a few days, and came up with another method of subtraction.  I call it the "3M" subtraction method because you turn the paper sideways so the 3's look like m's.  The method is time consuming because of extra writing required, but it is provocative because it is so repetitive and the carrying is sort of automatic after following the rules, and you get to do adding instead of subtracting, actually both in the same problem, so it is a curiousity.
Here is the video I made:  http://www.youtube.com/watch?v=Kk9U_pGvLU0


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