Hey,
There are month long study plans out there.
Magoosh does them as does GMAT pill.
Should be fairly possible to pull your score up in three weeks, though how much I don't know. I would say if business school is important do you really need to apply this year? Might worthwhile delaying so you can get a proper crack at the test.
Three basics things you need to do:
Understand how quant section works as GMAT has a funny question type. So read the strategy elements.
Learning priority is: times tables, percentages, ratios and number properties. Also learn the distance, time, speed formula. That should give your score a quick boost.
Timings and GMAT strategy: GMAT Manhattan has some good posts on timing strategy and and other general GMAT strategies.
Verbal: do the videos on basic critical reasoning and comp strategies. Should help with verbal score. And give yourself a basic refresh on grammar for sentance correction.
If you risk a low quant score: spend some time on the intergrated reasoning section; it's not yet adaptive and possible to get high score easily by understanding timing strategies. GMAT Manhattan also very good for this.
Four do one practice a week. Use that to guide your prep.
Ps I used
magoosh for my GMAT study.
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