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




Do you teach this subtraction algorithm?
Posted:
Nov 16, 2004 5:26 PM


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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