A long time. It is usually gone in 5-7 days, but if you have been using for a long time, it may be detected up to two months later. This is unfortunate, because people know it stays longer than other, more dangerous drugs and people may then decide to use these at the beginning of a weekend.
Depends. But in general, about 3 weeks.
Drug Testing. The amount that an individual smokes greatly effects the how long a test will be positive, as well as the cut off level of the screening test. Smoking one or two joints occasionally will only be positive for a day or two. Smoking 5-10 joints a day daily will likely be positive, if you stop for 5-7 days. Those who smoke 10 or more a day, and have been for years will be positive for months.