Thanks so much for your detailed explanation.

"Dave Peterson" <petersod@verizonXSPAM.net> ???
news:431DE86D.7B405545@verizonXSPAM.net ???...
> Depends on what calculation you're doing.
>
> If you have a couple of text dates in A1 and B1:
> '9/6
> '9/9
>
> Excel will do it's best to coerce the value to numbers in a formula like:
> =b1-a1
>
> Those arithmetic operators really help.
>
> But other formulas won't do that coersion:
>
> =SUMPRODUCT(--(A1:A10=DATE(2005,9,6)),--(B1:B10="red"))
>
> =======
> You can see it with a non-date example.
>
> Put
> '1 in A1
> '2 in A2
>
> =a1+a2 in A3
> =sum(a1,a2) in A4
> =sum(a1+0,a2+0) in A5
>
>
>
>
> 0-0 Wai Wai ^-^ wrote:
> >
> > "Dave Peterson" <petersod@verizonXSPAM.net> ???
> > news:431D89E0.DDC629C8@verizonXSPAM.net ???...
> > > If you're typing these values into the cell, you can either prefix them
with a
> > > leading apostrophe:
> > >
> > > '11/7
> >
> > Something I wonder:
> > If you do so, then excel should treat "the date" as **text**.
> > And you cannot use it to do calculations (eg calculate the date difference
> > between one and another).
> >
> > But when I tried it out, it is not true. Calcuation can be made.
> > How come?
>
> --
>
> Dave Peterson