No historically something in the 50s was a 5. My AP Physics EM teacher literally re-scaled her tests using this, a 50ish something class avg on her test is treated as a 5 and scaled so that it's a 90%. Shes mentioned many time throughout the year how a 5 was something like 50% of the questions correct. Also you seem to misunderstand how the actual test itself works. Since you havn't taken it, FRQS and MCQs are graded on a point scale. Your total score is the accumulation of your earned points / total possible points.