Re: virus: hey Eric

Eric Boyd (
Tue, 30 Mar 1999 13:24:53 -0500


From: Jim <>
Could you help me with a bit of math. If I take a three digit number then reveres it so now I have the original number and a new number generated from its reversal and then subtract the larger number from the smaller. Is it possible to tell what the starting number was just from the answer. Thanks for your time>>

My first guess would be no, but you better let me try:

consider a 3 digit number


it "reverse" is


the difference between them is

absolute value (cba-abc)

which could be


except that, obviously, either c-a or a-c is negative. Since we are assuming that the above is possitive, c-a is positive, and thus a-c is negative. Therefore we must carry the one from b-b, which carries the one from c-a and the answer is


which gives us two equations in two variables -- you could solve for a and c (in theory), but the value of b is unrecoverable.

Conclusion: it's not possible, just as I thought.