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Old 08-27-2016, 01:45 AM
gigi gigi is online now
Join Date: Apr 2000
Location: Flatlander in NH
Posts: 25,385
Originally Posted by Folly View Post
The second one is a variation or consequence I guess of 'casting out nines'.

The digits, even when reversed, will add to the same number and the result when subtracted will always be divisible by 9.
And that's how we bookkeeper types know we made a transposition error -- we're off by an amount that is divisible by nine.