Practice is one way. Another way is to try to Memorize as much info/formulas as possible. Here are a few suggestions: what-arithmetic-should-i-memorize-80128.html
Since it is math, it does not matter too much if you use OG or another source - you can get Kaplan
, MGMAT, PR, or others and just get Walker's GMAT Timer
and push yourself to do a question in under 1.5 mins. If those are easier ones, push to have them done in 1 min.
You can also look into the GMAT CLub Tests
- these are designed for 700+ applicants and those looking to score 50+ on math. The questions are harder than most other materials.
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