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Topic: Do you teach this subtraction algorithm?
Replies: 1   Last Post: Nov 19, 2004 12:42 AM

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juuitchan@hotmail.com

Posts: 26
Registered: 12/13/04
Do you teach this subtraction algorithm?
Posted: Nov 16, 2004 5:26 PM
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I think that this would be a great subtraction algorithm for those
whose attention wanders, because it is a "digit extraction" algorithm.

Example: 1776
-1492
-----

By inspection, the answer is three figures.

1776
-1492
-----

Hundreds' digit: 7 minus 4 is 3, but since 76<92, write one less, that
is, 2.

1776
-1492
-----
2

Tens' digit: 7 minus 9... we are working mod 10, so make this 7+1=8.
As 6 is not less than 2, leave this 8 unchanged.

1776
-1492
-----
28

Units' digit: 6 minus 2 is 4. Result: 284.

I like this method because if your attention wanders, it matters
little, as each digit is calculated independently of all others.
Charming, huh?

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