Mathimatical equations in PHP

Ok... I have a site that is for a football game and people play each other then report who is the winner and loser. Well, I want to inject some excitement a bit and do some stats, like Passing averages per game and rushing average per game. The problem is that it will need to make the total yards then divide them by the number of games they played. How would I do that? Also would I need two rows, one for total yards and one for averages? or just one row just for the averages?