There is no such mathematical formula for what you "need" to score on the OAT to get accepted. In my opinion, if you are prepared you should score no lower than 300 on any section. Admissions committees have noted that the trend for OAT scores coincides with your gpa, for example, if you have a 3.6 GPA your AA would be around a 360 and 3.0 around a 300. If there are vast differences you will most likely be asked during your interview to explain what happened. Also, if you have a "weaker area" in your application, for example C's in organic chem, make sure you excel in that section of the OAT.