Hi Gigabits,
Due to the CATs scoring algorithm, which presents increasingly difficult problems as you answer questions correctly, and easier ones as you answer incorrectly, it is impossible to correlate a score to number of problems missed.
There is a good description here:
https://www.beatthegmat.com/how-are-the- ... 12733.html
If you are scoring 20th percentile in Verbal right now, though, I wouldn't spend too much time focusing on the mechanics of the test. The tricks and tips presented by most GMAT prep programs will not help you improve your vocabulary or your grammar, so you would be best working on those on your own before seeking GMAT specific tutoring or studying from GMAT books. Ideas would be to take an English class at a local community college (pretty affordable), purchase an English grammar book (I recommend Strunk and White's Elements of Style), or hire a private English tutor.
Best wishes,
Tatiana
Tatiana Becker | GMAT Instructor | Veritas Prep
