Could There Be 8 Days in a Week?

Date: 04/24/2008 at 22:20:24
From: Gina
Subject: How many days are there in a week?

I know that there are 7 days in a week, but my question is, let's just 
say it's a Tuesday, if someone says, "Oh I can't wait till next
Tuesday to see my boyfriend, I have to wait 8 days" is this correct if
we are not considering the hours into this theory....?

I think it is but I'm not sure.  My theory is if it's Tuesday and you
have to wait till next Tuesday, so Tuesday 1st day, Wednesday 2nd day,
Thursday 3rd day, Friday 4th day, Saturday 5th day, Sunday 6th day,
Monday 7th day and Tuesday 8th day.

Could that be correct?

Date: 04/24/2008 at 23:00:50
From: Doctor Peterson
Subject: Re: How many days are there in a week?

Hi, Gina.

Different cultures would answer the question differently.  Some count
inclusively (think of the "octave" in music, which counts "do" twice),
while others count exclusively (as we usually do in our culture).
Mathematically, the exclusive count is more reasonable: Starting on
Tuesday, one day later is Wednesday, and so on, until 7 days later is
the next Tuesday.  Here we are actually counting INTERVALS--24-hour
periods from any given time on the first day until the SAME time on
the last day.

But it also makes sense for other purposes to count inclusively.  I
just mentioned "the first day" and "the last day"--those could well
be called Day 1 and Day 8, respectively!  If you count every DAY of
which any PART is included in your interval, then Tuesday to Tuesday
includes 8 days, not just 7.  It just doesn't include ALL of the two
Tuesdays; on the average it would include half of each, which is why
the actual time interval is only 7 days.

So neither answer is right in itself, and neither is wrong in itself.
The question is, what do you want to DO with your count?  If you're
going to use it mathematically, say, to find how far you can drive in
those days, you might find the exclusive count better; but in reality
you would have to be more careful in measuring time, and determine how
many hours of the first and last days you would be driving--the time
from Tuesday morning to the next Tuesday night allows a lot more
driving than the time from one Tuesday night to the next Tuesday
morning (effectively only 6 days!).  For other purposes, say, how long
a DVD can be taken from a library, you go by whatever rules are
established; in that case, very likely they go by how many closing
times elapse, which amounts to the exclusive count.

So that leaves me with the question: Why do you ask? 

And is it a Tuesday morning or evening when you talk about seeing your
boyfriend?


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