Quote Originally Posted by Ibar69
i.e. If it takes 30 days to get traces out of a persons level and they have to pass at 49 ng/ml. Does that mean 49 ng/ml * 10 days would be 98. 98 ng/ml * 10 more days = 196. And 196 * 10 more days = 392.

So the average daily smoker has a ng/ml level of 392? I may be totally off basis but I am curious what a generalized average ng/ml level of a daily smoker is.
You're very close. Because the half-life for THC varies from 0.8 days to 10 days, depending on the person and several factors from diet, physical activity level, body fat percentage, genetics, metabolism, etc., it is better to express it in terms of half life and not days. Also, most people work half-life the other way around.

So, let's say it like this. If you start with a level of 392 after 1 half life your level will be 196, after 2 half lifes your level is 98, after 3 half lifes your level is 49. Not all people start off at 392 and some people's half life is very short, 1-2 days, while others is very long, 7-10 days.

I've seen it stated that a one a joint a day smoker (not after 1 joint but someone who regularly smokes 1 joint a day) of medium grade pot has a urine level of 200-700 nanograms per ml of THC metabolites. Don't have a link or remember where I saw that, sorry.