[geeks] I know this wasn't taught in American schools...

[Jonathan Patschke]

On Wed, 5 Jan 2011, Jonathan J. M. Katz wrote:

> I saw this earlier today and was stunned. A pretty simple/easy way to
> perform multiplication.
>
> http://www.youtube.com/watch?v=e-P5RGdjICo

The system I learned in 5th grade or so works really swiftly with 2-digit
numbers, but is less useful with larger numbers:

   1) Multiply ones-digits; the result is the ones-digit of the answer.
      Hold onto the carry.
   2) Multiply the ones-digit from one number by the tens-digit of the
      other.  Add to the product of the other ones and tens digit.  Add the
      carry from step 1.  The ones digit of the sum is the tens-digit of
      the answer; hold onto the carry, if any.
   3) Multiply the tens-digits.  Add the carry from step 2.  The result
      comprises the remaining digits of the answer.

It may sound clumsy, but it's very fast and keeps very little state in
play (just the carry-accumulator), which makes it very easy to do
multiplication without scratch paper.

-- 
Jonathan Patschke  |
Elgin, TX          |  Sent from your rooted trendy mobile device.
USA                |