First of all, before I begin, this post owes a great deal to the detailed GMATPrep research done by the great
Bunuel. If you haven't read
this post by him, then do so immediately.
Ah, the mysterious GMAT scoring algorithm. None of us can pin it down precisely, because the GMATPrep tests are not quite the same as the actual thing. But we can certainly try, and the GMATPrep software (along with our anecdotal experiences of taking the test) is nevertheless the best evidence we have to judge the algorithm of the actual GMAT.
To start, it is important to know that while all of the questions on the GMATPrep tests do count toward your score, up to 25% of the questions on the GMAT are experimental--you won't know which ones they are, and they don't count toward your score. So keep in mind that on the real GMAT, there is a roughly 1 in 5 chance that the question you are looking at doesn't count.
There are two main principles at play in the GMAT algorithm:
1) Earlier questions count much more than later questions.
2) The GMAT gives you a severe penalty for getting multiple questions wrong in a row, and for not finishing.
One of the main conclusions of Bunuel's analysis above, for example, was that the best way to maximize your GMAT score with the fewest number of questions correct was to get "two right, one wrong" for the duration of the test. Think of it as "two steps forward, one step back." The reason why this works so well it because it maximizes your damage control by never getting more than one question wrong in a row.
AT ALL COSTS, TRY TO AVOID GETTING 3 QUESTIONS WRONG IN A ROW (especially in the first 2/3 of the test)! THIS IS SURE TO SABOTAGE YOUR GMAT SCORE.
A couple pieces of advice as it pertains to Quant:
1) Take an average of 2.5 minutes per question for the first 1/3 of questions (1-12), 2 minutes per question for the second 1/3 of questions (13-24), and 1.5 minutes per question for the final 1/3 of questions (25-37)
2) If you had to guess on your previous question, or you didn't trust your answer, then try extra hard on the next question. This is especially true if you had to guess on the last two questions!
3) Always leave yourself enough time to finish, even if it means blindly guessing.
Are you having trouble finishing on time?
1) If you are going for a
700, consider turning the GMAT quant into a 30-question test. That way you get a full 2.5 minutes per question. Simply guess on the last 7.
2) If you are going for a
650, consider turning the GMAT quant into a 25-question test. That way you get a full 3 minutes per question. Simply guess on the last 12.
3) If you are going for a
550, consider turning the GMAT quant into a 20-question test. That way you get a full 3.75 minutes per question. Simply guess on the last 17.
Yes, these are extreme measures, and they are not guaranteed to work (you need to get most of the questions right that you do answer). But it is meant to show you how "front-loaded" the points on the GMAT are.
If you have more time than expected, then I would suggest that you try every other / every 3rd question in the part that you had planned to guess your way through. This will help you avoid getting too many questions wrong in a row, which, as I have repeatedly emphasized, is key to maximizing your GMAT score.