Thursday, September 20, 2007

The Govt's Favourite- Multiplying and "Procreating"

It is indeed easier to multiply these as decimal numbers 177 by 23, but the Romans also had a multiplication method of their own. It was probably discovered by trial and error, and it always worked, though the Romans did not know why.

Here the method is described, and its secret explained. The Romans started by writing the numbers next to each other. Of course, they used Roman numerals--but to make it clear in what follows, here decimal notation will be used throughout. Suppose we need to derive

177 x 23

After writing down the numbers (here the multiplication sign was added), halve the first one and double the second, writing the new numbers below the preceding ones. If the number being halved is odd, just ignore the remainder. Repeat this operation as long as you can:

177 x 23
88 46
44 92
22 184
11 368
5 736
2 1472
1 2944

Now cross out in the second column all numbers where the corresponding number in the first column is even:

177 x 23
88 46
44 92
22 184
11 368
5 736
2 1472
1 2944

Then add up the remaining numbers:

23 + 368 + 736 + 2944 = 4071

Some fun before the Death Varder steps in?

4 comments:

WaterLearner said...

Doesn't really makes sense why it works huh?

mr fong said...

Haha, not even to me :P

To be fair and honest, there is a solution to the discovery of the method that is not revealed in the post,haha..

Sam Chan said...

Hi Winston,

That's indeed a funny and interesting method. However, it only can work for multiplication by 23 - right?

Best Wishes
Let's Acquire Wisdom and Live with Passion

mr fong said...

Hi Sam, thanks for bothering to read these mumbo-jumbo,lol!

Anyway, it can work elsewhere apart from 23. Hope this is helpful.

Thank u for your participation, I think I'm posting too irregularly now... :(