Formula help

I was able to use your sample to SUM up my numeric fields. But I use this form as a QA database to score call center agents. How do I convert my sum of points into a score as a percentage of the total possible points? I can sum th epoints they got, but how what formula do I use to say:
sum / Xnbr = XX%

Example:
sum - 13 points out of 15 so I need formula that returns 88.66%.
rgarcia