Tricky Math

External Since: Jun 22, 2004 Posts: 756

Got this from a friend for all you Math Pundits here.....

Click on the little guy on the right bottom corner to go to the
next page.
http://digicc.com/fido/

How do they do that?
--
Purrt the ghatta
Part-time gryphon
Disciple to the Goddess of Chocolate
Owner of a full Pedant's licenc/se
Goddess of Impertinence
Snikkrish the Tearer
Carpe Bean

External Since: Jul 14, 2003 Posts: 104

On Sat, 18 Oct 2003 14:57:03 GMT, "Purrt" <ivaf RemoveThis @ptd.net> wrote:

>Got this from a friend for all you Math Pundits here.....
>
>Click on the little guy on the right bottom corner to go to the
>next page.
>http://digicc.com/fido/
>
>How do they do that?

Nicest version of this I've seen in a long time.

Here's how they do it : Basically, the sum of the digits of the
number after subtracting will always be 9 (or a multiple - 18, 27...)
Then they add up the digits you gave and figure out the remainder.

It's a variant of a handy trick in accounting. If you're out of
balance by an amount divisible by 9, you've transposed digits
somewhere, most likely. If it's divisible by two, check signs on
entries 1/2 that amount.