I feel like such a doofus asking this simple question!

Excel 2003 .xls spreadsheet

I have a large area, encompassing several columns. I'm trying to figure out what percentage each column's total sum is of the whole total sum.

The formula I'm using is

=(SUM($A$3:$E$10000)/(SUM(A3:A10000)))

This evaluates out to 325.5/6.25, and the answer is 52.08, which I assume is correct, but isn't the information I want! If I format it as a percentage, I get 5208%. That is not correct.

Can anyone help me? Thank you very much!
Susan