On your first point, you are correct. The GMAT is very similar to the GRE in terms of the math you need to know. If you can score in the 90% on the GMAT then you should do very well on the GRE.
At the same time, it wouldn’t behoove you to be too cavalier about the differences between the two tests, especially because brushing up on the format of the GRE shouldn’t take more than a few hours.
A few important differences to keep in mind: the GRE provides an on-screen calculator (you will have to use for at least one problem) and there are a variety of question formats not found on the GMAT. Multiple answer questions state that any number of answer choices can be correct (e.g. you can have answer choices A-G and you will have to select the letter or letters that answer the question). Finally, there are also fill-in-the blank question. While the math should not be too difficult, solving a question without having recourse to the answers may force you to tweak your approach.
Again, spending a day going through the ETS revised GRE manual and/or taking the ETS PowerPrep test should be all you need: http://www.ets.org/gre/revised_general/ ... 2/download
Good luck, and let me know if I can answer any other questions!
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