Author

Topic: For math geekshow do they do this?

snupy
BlabberMouth, a Blabber Odyssey
Member # 1211
Member Rated:

posted June 19, 2006 12:25
http://digicc.com/fido/
 "I just ordered an extralong straw to avoid accidentally doing a situp"Jay, Modern Family
Posts: 4269  From: UK, via Chicago  Registered: Mar 2002
 IP: Logged



Spiderman
Solid Nitrozanium Superfan!
Member # 1609
Member Rated:

posted June 19, 2006 12:42
Fascinating.
The sum of the digits of the subtracted number always equal 18. By providing the site with the other digits of the number, it's easy enough to deduce what the remaining digit is.
I'm not entirely sure just *why* those digits add up to 18 though.
Clever, nonetheless.
Edit: dnm: argh, you would have to just paste a link to the solution wouldn't you? Referring to someone elses solution is just too boring.
 Math problems? Call 1800[(10x)(13i)^2][sin(xy)/2.362x]
Posts: 846  From: Chicago  Registered: Aug 2002
 IP: Logged


drunkennewfiemidget
BlabberMouth, a Blabber Odyssey
Member # 2814
Member Rated:

posted June 19, 2006 12:47
quote: Originally posted by Spiderman: Fascinating.
The sum of the digits of the subtracted number always equal 18. By providing the site with the other digits of the number, it's easy enough to deduce what the remaining digit is.
I'm not entirely sure just *why* those digits add up to 18 though.
Clever, nonetheless.
Close. The number is always the difference between the sum of the digits and next multiple of 9.
Posts: 4897  From: Cambridge, ON, Canada  Registered: Jun 2004
 IP: Logged


Spiderman
Solid Nitrozanium Superfan!
Member # 1609
Member Rated:

posted June 19, 2006 13:02
quote: Originally posted by drunkennewfiemidget: quote: Originally posted by Spiderman: Fascinating.
The sum of the digits of the subtracted number always equal 18. By providing the site with the other digits of the number, it's easy enough to deduce what the remaining digit is.
I'm not entirely sure just *why* those digits add up to 18 though.
Clever, nonetheless.
Close. The number is always the difference between the sum of the digits and next multiple of 9.
Yes, after playing with it a bit more, it quickly became evident that my arrival at the number 18 was correct, to a point, but not adequate to account for smaller numbers and numbers with small digits (or larger numbers for that matter).
It's a delicious oddity that the absolutely value of the difference between two permutations of a set of digits always equals a multiple of 9.
Oh, and now I see you've posted a solution. Lovely.
 Math problems? Call 1800[(10x)(13i)^2][sin(xy)/2.362x]
Posts: 846  From: Chicago  Registered: Aug 2002
 IP: Logged


snupy
BlabberMouth, a Blabber Odyssey
Member # 1211
Member Rated:

posted June 21, 2006 16:50
fascinating...like a foreign language, but fascinating.
 "I just ordered an extralong straw to avoid accidentally doing a situp"Jay, Modern Family
Posts: 4269  From: UK, via Chicago  Registered: Mar 2002
 IP: Logged


Stormtalon
Mini Geek
Member # 1163
Member Rated:

posted June 23, 2006 14:32
I think it has to do a lot with the fact (haven't found a formal proof yet  then again, haven't looked either) that:
For every numbering system of base (n) utilizing numerals 0 thru (n1), the digits in each multiple of the terminal digit (n1) when added together always equal a lesser multiple of (n1).
So, multiply 9 (decimal system) by anything. Add the digits. The result is a multiple of 9. In hexadecimal, the same holds true for multiples of E. Haven't worked up thru numbering systems beyond hex, yet, but I'm sure it continues to hold true.
If someone can find a formal proof, that'd rock. Otherwise, I'll probably email Polymath or Good Math, Bad Math blogs to see what those guys say.
 Those who are easily offended should be. And often.
WoW: The Crazy Ones
Posts: 73  From: Minnesota  Registered: Feb 2002
 IP: Logged


