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See, I knew someone would be able to do the actual mathematical thing. Nate Send a noteboard - 27/01/2012 09:08:02 PM
Essentially x0-x, where x is just a digit, not a number, will equal a multiple of 9.

That is sort of it, but going the wrong direction. 10x+x=11x; 11x-(x+x)=9x, by definition a multiple of 9. All other numbers between 10 and 99 are either:

10x+x+y, in which case 11x+y-(x+x+y)=9x, still a multiple of 9, or

10(x+y)+x, in which case 10x+10y+x-(x+x+y)=9x+9y, still a multiple of 9.


I understand how it works but had no idea how to express it in full mathematical style like that (hence using x as both a digit and a numeral in my example). You can tell I'm a writer because I try to explain math with words.
Warder to starry_nite

Chapterfish — Nate's Writing Blog
http://chapterfish.wordpress.com
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