The dutch grading system is on a 10-point scale, from 1 til 10, with at the UvA, a 5.5 meaning a pass. Grades are rounded (usually) by the .5, expect at the pass-fail point, where either you get a 5 or a 6.
The grades at the UvA are weighted, using Testvision, there is usually a ‘guessing chance’ counter-measure. More information can be found under the Exam Regulations of each course, on Canvas or via Studiegids.
Something that especially new students find difficult to realize, that equivilant to UK and US grade, an 8.5 is usually already a 1st/A, and receiving a 10 is extremely rare due to the grades being weighted. Therefore, a realistic expectation should be held for yourself, to balance student and study life.