You don't need to be a genius at math - I failed Math - you just have to times the stats by the weight... Like above, 420 strength (x1) = 420. 480 crit (x0.74) = 355.2. There, that's it.

There are, of course, tools with pre-set weights which aren't perfect but will help - Like AskMrRobot linked above by b4dcrc.