Half of Five is Four?

Date: 11/04/2004 at 12:54:40
From: Don
Subject: Half of five is four?

What's the only number system where half of five is four?

Date: 11/05/2004 at 12:15:10
From: Doctor Rick
Subject: Re: Half of five is four?

Hi, Don.

This is more of a riddle than a math problem.  The answer is really 
two "number systems"; one is the written-out English name of the 
number.  Can you see the other yet?

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

Date: 11/05/2004 at 12:32:39
From: Don
Subject: Thank you (Half of five is four?)

Thank you for your help.  I appreciate the clue to get the first part 
which made it easy to get the second part on my own.