Math-phobic students have always been a part of my life as a GMAT tutor, and I currently work with several New Yorkers who used to sweat profusely whenever they heard the words "slope" or "equation." One of my favorite current students is a 34-year-old actor who has taken exactly no math since high school, and he is raising all sorts of interesting questions as he starts to ascend toward a decent GMAT score. This particular guy (let's call him Mr. L... that's short for Law & Order, since he once appeared on an episode as the main victim) took a Princeton Review GMAT course, got a horrendous score on the math section (21, which is probably on the wrong side of the 10th percentile), demanded his money back from Princeton Review, hired a GMAT tutor in India (he was volunteering there at the time), and then managed to get a 33 on the math--a huge, huge improvement. (If anybody needs a GMAT math tutor in Ahmedabad, India, I can recommend a great one. Oddly enough, I also know a great auditor who lives there, too. And no, I've never set foot in Ahmedabad or anywhere else in India.)
Upon his return to NYC, Mr. L contacted me for GMAT tutoring, and we've been working together for about a month. His patience for the GMAT started to wane recently, and I suggested that he take a few practice math tests--not because I thought that he was almost ready to take the GMAT, but because I thought that online practice tests would keep him a little bit more engaged than paper-based practice problems.
And Mr. L pretty much crapped himself when he saw his first score: on a Manhattan GMAT test, he scored 40 on the math. I figured that it wasn't a complete fluke--Mr. L had improved by quite a bit. But he was highly skeptical, so I asked him to take another MGMAT math test. And he scored 40 again. Clearly, the 40 wasn't a fluke, unless you're skeptical of MGMAT's scoring (that's another topic entirely, but I usually find that the math scores are fairly accurate for students who haven't taken their course).
I haven't quite succeeded in convincing Mr. L that he deserved the 40, and here's why: on both tests, he got 20 questions right, and missed 17. In the American educational paradigm, getting just over half right usually means that you barely passed, which means that you suck. Mr. L couldn't really get his head around this: he missed enough GMAT math questions to suck pretty badly, but his score was higher than he ever dreamed possible.
So here's the deal: adaptive tests such as the GMAT and GRE are designed to make you miss lots of questions. (That's one of many reasons why taking these tests can be such a painful experience.) Each GMAT question is essentially assigned a difficulty level--if it helps, you can think of each GMAT question as, say, a "700-level" or a "520-level" question. The test basically tries to figure out the level of question at which you get 50% right. It seems logical that you might be able to get 55-60% of the questions right, and still get a decent score--your score is based on which questions you miss, not necessarily on how many you miss.
If you don't believe me, check out a recent entry in the official GMAT blog that addresses this issue. Or keep reading. Whichever you prefer.
If it helps, imagine that you're destined to earn the equivalent of a 650 on the math section of the GMAT. (For the sake of simplicity, I'm going to ignore some of the complexities of GMAT scoring. Forgive me.) The first question of the test will be a 550-level question (roughly), and let's suppose that you get it right. You'll get a harder question next, and you probably won't start to screw up consistently until you see a few 650- or 700-level questions. But it won't take too long to get to that level--if you get the first three questions right, the fourth question of the GMAT quant section will probably make you sweat.
Now, imagine that the fourth question is a 650-level question... seems reasonable enough, right? If you're a 650-level test-taker, you're likely to miss about half of the remaining 34 questions. I'm obviously making some gross oversimplifications here, but it isn't hard to imagine that you could get a 650 on the GMAT, or perhaps something even higher... without getting more than about 20 questions right.
My point is this: in all likelihood, you have a huge margin for error on the GMAT. As long as you don't fall apart at the beginning of the test, you can miss tons of questions, and still get a fantastic score. So when you see some crazy, indecipherable GMAT combinatorics problem, there's really not much harm in guessing and moving on--one missed question won't hurt your composite score by much, and you'll have plenty of chances to recover.
So if you're reading this, Mr. L... have I convinced you yet? You actually deserved those 40s, and we're not even warmed up yet. Crazy as it sounds, getting 60% of the questions right might be enough to get you wherever you want to go on the GMAT math section.