For technicality sake. 84/120 = 70%. 36 wrong on the test and still pass. 18 for each session (AM , PM) ~1.8 per vignette. You need 4/6 on 16 of the vignettes and 5/6 on 4 of them to pass. can someone confirm these assumptions
No. Nobody can confirm your assumptions. They are the best guess, but they cannot be confirmed because CFAI does not state the pass rate.
As a rule of thumb, you should be certain on the answers of at least 3 questions per vignette. Then if you guess the other 3 questions, the expected value for randomly guessed correct answer is 3/3=1. So it’s 4 x 20 / 120 = 67%. With some luck, after some CFAI curving, you can pass. 
Truth is we have no idea…it’s a new ball game with the three choices… unfortunately for us…we are the lab rats… they are testing on us… they have the excuse now with the three choices to even bring up the passing rate to 80%…unlikely but who knows… It’s out of our control…all we can do is make sure the AF posters get 90% passing rate…
I don’t think having 3 choices is going to bump the pass % by 10%, may be 1-2%. The reason they went to 3 choices (as is claimed) that vry few people picked the obvious wrong choice
thirty six
By getting them all right you will be guaranteed to pass. No has ever failed by getting every single answer correct. But then again, no one has ever received a perfect score.
I would say you can get 40 wrong and still pass. 67% seems like it should pass. I can’t image that 46% of the people last passed it last year got more than 67%.
To get a passing score, assuming its 70%, you can’t get more than 36 questions wrong. That’s the hard number. But lets say that you’ve finished the test and looking back, you realize you are absolutely clueless about 54 of the 120 questions. You can still pass! By sheer probability, you may get 18 out of 54 questions right, which leaves you with 36 absolutely wrong answers…of course this means you have to get the other 66 questions absolutely right!
I can probably get 40 correct, for another 40, I have 1/2 probability to get them right, for the last 40, I have 1/3 chance to get them right so my total score will be 40+20+12 = 72, which is 60% if I’m lucky, I may still pass. God bless me!