there's probably a number of different reasons...could you provide more detail?
these are the questions i'd ask:
- is english your native language?
- how long does it take you to complete verbal vs math questions? within the different types of verbal questions, how long is it taking you? e.g., does it take you longer to complete RC vs SC?
- what are you spending your time on? reading and understanding the question or working out the problem? if it's a math question - are you spending most of the time trying to solve the problem? if it's verbal, are you spending lots of time reading the question? are you re-reading verbal questions?
see how there's different questions you can ask to diagnose your problem? if you aren't already, you should time yourself on every problem you do and categorize each problem type so you can see exactly where you're spending your time. track if you got it right or wrong and identify for those questions which you spent >120 seconds on, did you get it right? sounds like you're doing this already.
once you've done enough problems, you should be able to identify which types of problems are taking you longer. you need to identify the root cause of your timing issues and then you can work from there. if it's because of math concepts, then you'll need to work on rules, formulas, etc. if it's understanding the content of a RC question, then you need a strategy for reading the passages effectively. if you have that figured out, then share a bit more detail so that you can get more helpful advice. otherwise, it's going to be hard to give good guidance.
http://gmatclub.com/forum/post558169.html#558169 - a compilation of b-school interview questions
http://gmatclub.com/forum/8-66345.html - my (detailed) gmat debrief
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