Why Commas after Every Three Places?

Date: 07/10/2001 at 00:30:27
From: Larry
Subject: Commas after every 3 places?

Why do we put commas after every three places in a number like 
200,000?

Thank you.

Date: 07/10/2001 at 05:28:55
From: Doctor Floor
Subject: Re: Commas after every 3 places?

Hi, Larry,

Thanks for writing.

The use of commas in large numbers is not necessary, it is a service 
to the reader. 

The commas are exactly in the right places to show thousands, 
millions, billions, trillions, etc., so they fit the way we pronounce 
the numbers. 

Also, it is quite comfortable to read numbers in parts of three 
digits, when you have to "spell" them.

Commas are not used everywhere in the world to do this job. It can be 
done by using spaces as well, so instead of 

      3,978,654,128 

one sometimes sees 

      3 978 654 128

In my home country, the Netherlands, the roles of dot and comma are 
reversed, so here we would write:

      3.978.654.128

and the decimal number 3.978 is written as 3,978 in the Netherlands. 
Be careful when you are outside your own country!

If you have more questions, just write back.

Best regards,
- Doctor Floor, The Math Forum
  http://mathforum.org/dr.math/