Hi Jordan
I don't really know why you would want to do this, but here is one solution.

If the column headers are in A1,B1, and C1 create 3 more columns in say
E1,F1 and G1.

Now, in cell E2 put the formula =IF(A2="",B2+C2,A2) and copy down as far as
you need.
In Cell F2 put the formula =IF(B2="",A2-C2,B2) and do the same.
Finall, in cell G2 put the formula=IF(C2="",A2-B2,C2) and also copy down as
far as needed.

As you fill in the data in the original cells, the new columns will populate
the required answers.

When completed you can hide the original columns.
This is a fairly ugly solution, but will work. Other option is to use VB

HTH
Michael.

In cell


"Jordan Smith" wrote:

I have three columns: "Number 1," "Number 2," and "Difference" (which
is Num 1 - Num2).

In a given row, I want to be able to enter any 2 of the fields and have
Excel calculate the 3rd one.

I.e.: (=x are the numbers excel calculates. The other numbers I type
in)
Num1 Num2 Diff
4 2 =2
=2 1 1
3 =2 1


How can this be done?

Thanks,
Jordan