Placement of Commas in Writing Numbers

Date: 10/22/2003 at 10:20:19
From: Beth Mearkle
Subject: Place Value

Why is the ones period named for the ones place value and why is the 
thousands period named for the thousands place?  Why is there not a 
hundreds period?

Date: 10/22/2003 at 12:26:46
From: Doctor Peterson
Subject: Re: Place Value

Hi, Beth.

We do, of course, have a PLACE for hundreds; but PERIODS are divided 
by thousands, to match the way we say numbers aloud:

  123,456,789 = 123 million, 456 thousand, 789 [units]

So each period is named for the value of its least significant digit, 
and each period contains three digits.  There is no real mathematical 
reason for doing this, apart from the value of consistency; it is just 
a good match with English (and most other languages).

You may be interested in the fact that in India, commas are put in 
irregularly, to match an irregular set of number names:

  Numbers in Hindi and Urdu
    http://mathforum.org/library/drmath/view/57179.html 

In their language, a lakh is what we call one hundred thousand 
(100,000), and a crore is our ten million (10,000,000). In order to 
match how they say numbers, they write a lakh as 1,00,000, and a 
crore as 1,00,00,000.

So, since we read numbers as "XXX thousand, Y hundred, ZZ", we could 
very well have chosen to write numbers as XXX,Y,ZZ. But I think it's 
good that we don't, because it would be confusing, and would not help 
much if any. Perhaps we were saved from that by the fact that we 
don't normally put a comma after "hundred" when we write out numbers 
(or a pause when we read them), so the comma did not seem necessary. 
Also, the fact that we say "hundred" within the other periods would 
force us to write X,XX,Y,ZZ, and we just don't need that many commas.

If you have any further questions, feel free to write back.

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