Are you taking the seminar with the exam? If so then many of your questions will be answered there. I hope you have some prior experience with welding and using a code. 3 Weeks isn't much time to get ready.

It has been 10 years since I took my exam, but I don't recall any "tricky" math questions. The plastic weld replicas I saw were not good. One in particular would be rejected just for being so ugly in the real world but the evaluation was for undercut only (which I had to call acceptable).

Maybe someone who has taken the exam more recently can give a better answer.
Anyway, best of luck to you.
CHGuilford