Basically, if I don't know what I'm doing by the halfway mark (1min on quant), then I decide whether I want to make an educated guess or a random guess. If I'm not behind in general, then I spend 30 to 60 seconds trying to eliminate some wrong answers before guessing and moving on. If I am behind in general and need to make up time, then I guess randomly and move on. And, yes, I will do this on question 6 if need be. Maybe I got the first 5 in a row right and 6 is totally a killer!
Also, when making a decision to go over time on a problem, I will go over (up to 30 sec) if I totally know how to do the problem but it's just long or convoluted for some reason and will take a little more time. I do NOT go over if what I'm thinking is, "Well, I don't really know what to do, but I'm sure I'll figure it out if I just spend a little more time..." I know from lots of experience that an extra 30 seconds is not going to magically turn a problem from "I'm not really sure" to "I totally know what to do." And I can't afford to spend more than an extra 30 seconds. So that's the end of that problem - guess (either educated or random, based on whether I'm behind) and move on.
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Stacey Koprince
GMAT Instructor
Director of Online Community
Manhattan GMAT
Contributor to Beat The GMAT!
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