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Topic: How does this work ? 


Has anyone seen this web site ? http://digicc.com/fido/ Im sure there is a simple answer to this puzzle but I cannot work it out.I don't want the answer I would just like to know if anyone knows how it works 


Cute website. It's a very old math effect. I don't think anyone will mind if I tell you that when you do that kind of subtraction, the digits must add up to a multiple of nine. Lots of other fun math stuff in this forum, check it out. Jack Shalom 


I do! DW 


Relax there Jack! That's my favorite secret...LOL 


That is definitely my favourite way to force a number to be a multiple of nine. Here's a hint to why it works (n>m): a*10^na*10^m=a*10^m(10^(nm)1)=9*a*10^m*111...111 where the last number has nm ones in it. /Tomas 


[quote]Here's a hint to why it works (n>m): a*10^na*10^m=a*10^m(10^(nm)1)=9*a*10^m*111...111 where the last number has nm ones in it. [/quote] That's easy for you to say . . . :) 


What is it about the nine that so many tricks involve him. will it work with 7 in a octali basis? Have fun ROi 


[quote] On 20060623 11:16, roi_tau wrote: What is it about the nine that so many tricks involve him. will it work with 7 in a octali basis? Have fun ROi [/quote] yes Gardner (who else) has written about it. N 