ammuseeruThis is what I know about experimental questions on the GMAT:
1) 9 out of 37 questions in the quant are experimental and 11 out of 41 questions in the Verbal are experimental. I don't have an official source for this number so this data could be wrong. I know the old GMATPowerPrep did not count 9 of the 37 quant questions so these numbers may be correct.
2) Experimental questions do not count towards your score. It is unlikely that you would be able to tell which questions are experimental and which are not. It is not even worth wasting your energy on it.
3) There is one circumstance where you can make a guess and that is if you are scoring really high(prior scores of 750 or so) and you see a question at #20 and it asks you to find the hypotenuse of a right triangle with sides 6 and 8. It is most likely an experimental question. I have experienced it in the real GMAT.
4) Official GMAC sources have also confirmed the following: "the process for experimental items is the same for every examinee and every instance. Each examinee will receive the same number of experimental items as every other examinee, without regard to current or past performance."
5) Based on this blog post, it seems that Larry Rudner may have disclosed more details about the experimental questions: "On the actual GMAT, the number of experimental questions may not be 1/4thas previously assumed. Or they may be of that proportion. This is a secret sauce that the folks at GMAC are not yet willing to reveal.
However, here is something that can help you “guess” better: the experimental questions will typically NOT be at the beginning or the end of the test. In other words you will typically get the experimental questions around the middle of the test (say questions # 10- #30)."
This was always my suspicion and I always recommends students to skip in the 10 to 30 range, if they encounter a hard questions. Of course, you can't afford to skip or let go many questions if you are targeting a high score.
I have given you what I know and the source of that information. Ultimately, you just have to focus on doing the best that you can, and ignore all this noise.
Cheers,
Dabral