I have taken 1 MAGMAT test, 1PR test, 1 GMATPrep test, and several Challenges.
I must say that GMAT Club challenges are the best of the lot for Quant.
Challenges cover *almost all* topics in GMAT Quant. The questions are TOUGH/TRICKY - basically make you think in the right direction.
Here is how I would go about utilizing the Challenges.
1. Start taking the challenges 4-6 weeks before your final test. YES you will need atleast 25 to 30 days to digest all of the information.
2. Spend time analyzing your mistakes.
3. Be sure to SPEND TIME AND ANALYZE EACH question. Initially you might take more time but its worth the effort!
4. Take a break after 5 Challenges. For the topics/areas - For eg. Mean/Median/Mode, Absolute values - you consistently miss questions, go back and STUDY THE FUNDAMENTALS.
5. Make a list of your errors in EACH category and review them once a week.
6. DON'T GET DISCOURAGED by your performance on the test. The ones who scored 98-99% on Challenges are GODs of QUANT - some of the smartest people on this planet. Don't compare yourself with others right from test1. After taking a few challenges, you will reach a stable range of scores.
Good luck!
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"To dream anything that you want to dream, that is the beauty of the human mind. To do anything that you want to do, that is the strength of the human will. To trust yourself, to test your limits, that is the courage to succeed."
- Bernard Edmonds