I smoked 3.5 grams (1/8 oz.) of marijuana about 7 weeks ago, over the course of one week. Before that, I had been clean for at least 6 months. I haven't smoked since. Will I likely test positive on a hair test?

Will minor levels show up, yes. What is the test for? What are the acceptable levels?

I agree, THC will be detected but at what levels is unknown. I doubt at a level that a habitual user has, but recent use will be indicated. It really depends on who you are being tested by, and the conditions you are being tested under.

A hair drug test is mean to show consistent use over time. A 1.5 inch sample, cut at the scalp line, will go back 90 days. When the lab gets the sample they pulverize it into a power so that 1.5 inch, you could say, would be averaged for that 90 day time frame. So my best guess is that you would be negative because that wasn't much use.