I think this is it. Whenever you do the subtraction you always come up with a number which is a multiple of 9. When you add the digits of a number the multiple of 9 you come up with a number which is a multiple of 9. So all that needs to be done to find the answer is add enough to the sum of the digits to make a multiple of 9. * To join/leave the list, search archives, change list settings, * * etc., please visit http://raven.utc.edu/archives/hp3000-l.html *