The MCAT is composed of four sections:
Chemical and Physical Foundations of Biological Systems
Critical Analysis and Reasoning Skills
Biological and Biochemical Foundations of Living systems
Psychological, Social, and Biological Foundations of Behavior
Each section is scored on a scale of 118 to 132 with a median section score of 125. The sections scores are added to give the total score, which ranges from 472 to 528, with a median score of 500.
The content and skills tested on each exam is consistent, but the specific questions and passages change from test to test leading to some variations in exam difficulty. The conversion between the number of questions answered correctly and the scaled score is specific to each individual exam to ensure that a student would get the same scaled score regardless of the specific version of the test they took. Statisticians at the AAMC make sure that the curves and MCAT scores are comparable everywhere and for every test date, which explains why it takes 30-35 days to get your score back after you test.
Thus, there is no direct relationship between the number of questions answered correctly (raw score) and the scaled score that is consistent across all exams. For a student to get a 515, they would need to answer more questions correctly on an easier version of the MCAT compared to a more difficult version.