[PLUG] How to get Latex to do my math for me

[John Jason Jordan]

I'm trying to create a table and have Latex calculate the width of the
columns, based on the fact that the table will be 568.8 points wide and
there will be two columns. The following blows up on me:

\begin{tabular}{|p{568.8/2pt}|p{568.8/2pt}|}
 \hline \hline

If I change the 568.8/2pt to 284.4pt it works fine.

I thought of doing the math prior to the table with something like 'let
x=568.8/2' and then just say xpt. But I don't know how to do that, and
it probably wouldn't work anyway.

Now, of course I can do math, in fact I can calculate the above in my
head. But sometimes it's faster to let the computer do the job.

Ideas and suggestions welcome!