The computer system will shut off when certain parameters are met. You must have >70 questions asked, and it must be clear that the applicant has either passed or failed. Once 70 is reached and you have not passed at that point, the system will continue asking questions until you have clearly passed or failed or you reach the maximum of 150 questions. And then it will shut off. Apparently there are also some applicants that are randomly selected to go the full 150, and some of those questions aren't scored because they're trial questions that may be included in future testing.
Bottom line is that you won't know until your results are released. The NCLEX is set up in a similar manner, and it's questions are adaptive. Therefore every exam is unique and will be the toughest exam you'll have ever taken, because that's what it does. I have no doubt that the current NREMT-P exam is also similarly adaptive.