The T-Score Formula. The t-score is a fraction. The numerator is the sample's mean minus mean of the group you are comparing the sample to, and the denominator is the sample's standard deviation divided by the square root of the sample size.
If you have smoked marijuana then the drug will stay for 3 to 30 days. This is normal for the common drugs. But in the case of marijuana, this can be detected even after a month in Urine drug test marijuana. Marijuana will stay in your system for 10 days if you have been smoking occasionally.
What About Other Drugs? How Long Do They Stay In My System? According to a survey by Quest Diagnostics, 50% of all drug test positives are for marijuana. What about the other 50%? The table below shows how long drugs other than marijuana typically stay in your system: