Commas in Numbers

Date: 09/13/2001 at 21:44:17
From: LaToya Clayton
Subject: Do commas change the value of a number

Why are we taught in grade school to put the comma after the third 
digit in a large number? (9,876,543,210). Why not the fourth digit? 
(98,7654,3210). And does the comma really change the number value?

Date: 09/13/2001 at 23:28:50
From: Doctor Peterson
Subject: Re: Do commas change the value of a number

Hi, LaToya.

The comma has no effect on the value of a number. All it does is make 
it easier for humans to read it. We put a comma every three digits to 
match the way we say numbers in English, by thousands. Your number 
reads naturally as 

   9 billion, 876 million, 543 thousand, 210 

Divided every four digits, you would want to read it as something like 

   98 myrion, 7654 myriad, 3210

(I made up the word "myrion," but "myriad" really does mean "ten 
thousand".)

The commas are purely for convenience.

- Doctor Peterson, The Math Forum
  http://mathforum.org/dr.math/