Most here have reported the biggest success with the MGMAT SC
book. If you still need help beyond that, perhaps you should try the books in the GMAT fiction
If you are struggling with the RC concepts, you should revisit the intro books. We have had many people report success with the LSAT books, but that applies to more advanced problems.
Regarding geo: The geometry questions on the GMAT (at the 600+ level) test your ability to either solve for an unknown or use simple proof to solve for an odd shaped object. The key with these problems is:
1. WRITE EVERYTHING DOWN. If you have a solid foundation in the properties of the various shapes, you can always solve the question. It's usually very indirect, none the less, it is not impossible.
2. SLOW DOWN and don't panic. The problems often look more difficult than they actually are. Knowns are sometimes not directly labeled and you must extrapolate from the knowns given to come up with the remaining knowns.
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