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Replies: 5   Last Post: Jun 15, 2011 10:45 PM

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 Ken.Pledger@vuw.ac.nz Posts: 1,412 Registered: 12/3/04
Posted: Jun 14, 2011 5:11 PM

In article
jbriggs444 <jbriggs444@gmail.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.

Ken Pledger.

Date Subject Author
6/14/11 Ashok. R
6/14/11 jbriggs444@gmail.com
6/14/11 Ken.Pledger@vuw.ac.nz
6/15/11 RGVickson@shaw.ca
6/15/11 cwldoc
6/15/11 Tim Little