Drug half life, its going to be on my test but the book doesnt really explain how to figure it up right. Like a question saying if your drug half life is 36 how many days would it take for the amount of drug to be 4 percent left in the body? Or what is amoutn of drug left in the body after 24 hours? This just confuses me b/c they didnt explain it well in class, and the book isnt helping at all! Any help would be greatly appreciated.