The GMAT scoring algorithm is somewhat of a blackbox. No one really knows how it works with certainty, except for GMAC.

All I can say is that I've seen other people in this community report similar 'hit rates' and still score well.

yes, almost everyone gets about 1/2 right and 1/2 wrong. Once you get above 700 or below 300, it starts to skew a bit - but it is still the case that you will get a lot of questions wrong. The algorithm is NOT "percentage correct"-based (the way paper tests are scored). Even if you score a perfect 800 - you're getting questions wrong on the test.