Search All of the Math Forum:
Views expressed in these public forums are not endorsed by
NCTM or The Math Forum.



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?
 submissions: post to k12.ed.math or email to k12math@k12groups.org private email to the k12.ed.math moderator: kemmoderator@k12groups.org newsgroup website: <a href="http://www.thinkspot.net/k12math/">http://www.thinkspot.net/k12math/</a> newsgroup charter: <a href="http://www.thinkspot.net/k12math/charter.html">http://www.thinkspot.net/k12math/charter.html</a>



