Scoring Question

so trying to understand....

is each question on the test assigned a certain percentage that testtakers have gotten correct? so there are such things as a 700 question, a 750 question, an 800 question?

Or are they grouped by just certain levels, so all the 700 level questions are of equal difficulty, and the more you get right the higher the score?

So if you are at the 750 level after question lets say 20, would you get a 760 level question? and then if u get that wrong a 740? get that right back up to 750? but that means you can go back and forth right and wrong and still get a 750.

Another example if you get the first 30 questions right, would the last 11 questions be lets say an 800 level question meaning that over 99.9 % of the respondants answered eac of them incorrectly?

I am not sure if that made sense, but just trying to figure it out.