Hi denniscool, I'm glad to hear you asking about what GRE resources you need to tackle the GRE rather than just trying to use your existing GMAT books. At Manhattan GRE, we have noticed that some people attempt to study for the GRE using exclusively GMAT guides, and this isn't necessarily a good solution. While there is overlapping conceptual content between the GMAT and the GRE, there are key differences in the application of those concepts that we try and point out to our students. First and foremost, the GMAT has a more challenging quantitative section, while the GRE has a more vocabulary intensive verbal section, so you want to tailor your preparation strategy based on that knowledge. It is probably useful to take one of the free PowerPrep tests provided by ETS (the organization that administers the GRE) at the beginning of your GRE studies to become familiar with the differences in difficulty and format when comparing the GRE and the GMAT. Then, you can use that knowledge of your GRE weaknesses to decide what types of guides to buy.
The verbal section on the GRE differs heavily from the GMAT. The GMAT verbal questions are truly not comparable to the GRE Antonyms, Analogies, and Sentence Completions, so you definitely want to get new guides to focus on those areas. Also, in terms of timing out the test, the reading passages in the GRE are very different lengths from those on the GMAT, so be prepared to adjust your timing accordingly on test day (pacing is very important!).
On the math side, the Quantitative Comparisons and Data Interpretation questions are unique to the GRE, replacing the Data Sufficiency type of problem seen on the GMAT. Be sure to pick up guides that cover these Quantitative Comparison questions.
It sounds like you are on the right track. I would just recommend that you take those free PowerPrep tests from the ETS website to make sure understand the subtle differences between the two tests. Good luck in yours studies, and good luck on your exams.
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