Also, be aware that the percentage you get wrong has very little to do with your final score. Eric mentioned this in his post, but I just want to elaborate: DO NOT base your progress on the number of questions you get right.
The difficulty level of the questions you get right or wrong is a far greater indicator of your score than just the raw number you get right or wrong - COMPLETELY different from the way we were tested in school.
Most people get roughly half the questions right (and roughly half wrong, of course) on the test - and they score anywhere from 300 to 700 with that performance. Think about that - you can score in the 90th percentile and get only about half the questions right. (This is approx. of course - maybe you'll get 56% right or something like that.)
The difference lies in the difficulty levels of the questions. Below 300 and above 700, you'll start to get more wrong or more right, respectively - but even a perfect score, 800, means you're getting around 5 or so questions wrong in each section.
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Stacey Koprince
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Manhattan GMAT
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