You should definitely follow up each chapter with OG problems. Our book is designed to teach the concepts you need, but it is important to practice these concepts in the context of real GMAT problems. Now, here's how to avoid "wasting" problems:
1) Do only a few problems at a time--for instance, 5 problems timed at about 6.5 minutes. Make sure you have committed to an answer for each problem.
2) After you complete your timed set, DO NOT look up the answers. Take some time to go through the problems again. Here's what you should be looking for:
*Why is each answer choice right or wrong? (Be as thorough as possible here.)
*How is the topic from the current chapter tested? What are the indicators that this topic is an issue?
*What answers can you eliminate using this issue?
*What other topics are tested? (Try to come up with eliminations for each topic.)
*Are there any traps or non-issues?
*Are there any choices that I don't like, but that I can't explain?
*Is there anything I didn't like about the answer I chose?
*If you were stuck between two choices, pay careful attention. How do the choices differ? What specific things make one different from the other?
3) Make a final deliberation--do you need to change your answer?
4) Check the answers and see how you did. Count a problem as wrong if you missed it initially, but make a note if caught the error in review.
5) Now that you know the answers, review again as needed. If you missed a problem, try to see what you did wrong. Don’t go to the explanation until you have gotten as far as you can on your own.
6) Check the explanations for all problems. On problems you got right, use the explanations to verify your thinking and check for any issues you might have missed. On problems you missed, see if there are concepts you need to review, or usages that seem to represent an exception to a rule.
7) Create a list of key takeaways and questions. What did you do well? What areas or topics do you need to review? Are there things that didn’t make sense in the problems or explanations? If needed, take your questions to the forums, or to a tutor.
As you can imagine, this process is rather time-consuming, but let me assure you that it will all be time well-spent! This way, you can also squeeze the most out of your first run through the OG. (Yes, you will probably want to run through these again. Once you know the material better, you will be able to analyze the problems on a deeper level. If you focus on the approach above, it won’t matter that much that you’ve done the problems before.)
In any case, you certainly don’t have to do *all* of the assigned problems in each topic. Start with a few of the lower-numbered problems and see how you do. You may want to return to some of them later. You may also want to save some problems in each topic, so that you can do sets of mixed problems once you’ve covered all the topics. Of course, you can also apply this approach to the other areas of the test. (In fact, you want to make sure that you don’t focus too exclusively on SC, or on verbal in general. Keep your practice balanced, even if you are strong in quant.)
If you’re still concerned about running out of problems, remember that there is also the Verbal Review (2nd edition). You can also purchase back editions (e.g. OG 10th
edition, which has some overlap, but lots of problems you won’t have seen), or download pdfs of old paper tests from mba.com. ($30 for a set of 3) You should also have access to the SC question bank on our website.