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O wise ones:
  My friend just sent me a math-related "mind-reading" site, and I have figured out 
how it works, but I can't prove it. If you want to look at it first, here's the 

  The directions say to choose any two-digit number, add the digits together, and 
subtract them from the original number.  Then you look at the list of numbers and 
find the matching symbol for the result.  You do this without entering anything 
into the computer.  Then you fix the symbol in your mind and click on the circle, 
which then reveals your symbol.  
  I tried this with several numbers and always came up with the same symbol.  I 
noticed that the final numbers were always multiples of nine.  So here is my 
question.  I think that any time you add the digits of a two-digit number together 
and subtract from the original number, you will get a multiple of nine.  Is that 
true?  How do you prove it without going through this process for every two-digit 
number?  I'm pretty sure there's an n+1 involved here somewhere!
  Thank you very much!
  Cindy Denning
  once and future librarian
  Collinsville, TX

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