If you look at Barron's you'll find that it's impossible to get a 30 in some sections based on the standard score to raw score conversion chart. According to them, its not possible in bio & g. chem. I'm not sure whether this is true for the actual test. Also as your score rises, some scores are not possible. Bio for example, there are 40 questions, a score of 23, 25, 27, 28, & 30 are not possible these scores are skipped because each question right has a exponential impact. The scoring chart looks like a bell shaped curve. With the average score for 20 points right is a 17.