In article <firstname.lastname@example.org>, jbriggs444 <email@example.com> wrote:
> On Jun 14, 8:04 am, Ashok <nils_von_nostr...@yahoo.com> wrote: > > .... > > When I am traveling by road, I frequently add up numbers on vehicle > > license plates. For instance, if I see a license plate with the > > numbers. EBD 2498, then I ignore the alphabets and add 2 + 4 + 9 + 8 = > > 23 and then 2+3 = 5.... > > http://en.wikipedia.org/wiki/Casting_out_nines > > The method that you have discovered is (or was) common knowledge > before the advent of computers. Mathematically it is a computational > trick to come up with the remainder of a number upon division by > nine without having to actually do long division. > > It is (or was) one of the standard tools in a book keeper's bag > of tricks when the books don't balance. Take the discrepancy, > cast out nines and see if the result is zero. If so then you > may have transposed digits somewhere.
I've nothing to add to that excellent answer; but the OP deserves to be complimented on his mental arithmetic. Adding up numbers like that is becoming a rare skill, especially if it's a background mental activity while driving a car.