# Re: Stupid Arithmetic Tricks

```also sprach Branden Robinson <branden@debian.org> [2002.03.28.1831 +0100]:
>> If I'm given a long column of one or two-digit numbers to add up (on
>> paper), I go down the ones column and strike out all complementary pairs
>> that add up to 10, e.g., 1 and 9, 2 and 8, 3 and 7, etc.  For each pair
>> that I strike out, I make a tally mark or just keep track mentally.
>> Odds are you won't be left with very many digits to add up.  So you do
>> that, carry the one if need be, and then add your tally marks to what
>> you're carrying.  So if I struck off 4 complementary pairs that add up
>> to 10 and I was carrying a one, I'm now carrying a 5.  You can then
>> repeat this process for the tens column.  In theory this works for
>> arbitrarily long numbers, but with numbers > 99 paper space becomes a
>> concern.  This technique is much, much faster than manually adding each
>> digit to the one below.  At least in my experience...

On Thu, Mar 28, 2002 at 11:04:28PM +0100, martin f krafft wrote:
> not meaning to push you off your cloud, branden, but that's how it's
> taught to first-graders over here in germany ;)

Could it have something to do with the story of Gauss adding up the
numbers from 1 to 100 as a child in the 1700's?

Cheers,
Bill

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