If I give enough time, I correctly answer most CR questions.
Stop thinking this way right now: if I can spend as much time as I need, I can get these right. That prioritizes accuracy over timing - but that is NOT how this test works. Both measures are equally important.
This test is not just testing you on whether you know the material and can answer the questions. It's also testing you on whether you can set priorities and manage your time appropriately (as any good businessperson should know how to do!). Think about your average workday - sometimes there are things you have to leave till tomorrow or next week, right? Sometimes there are things you have to give to somebody else or say you can't do.
You may want to think of this as a tennis match, not a test. You're going to win some points and the other guy is going to win some points; you're not going to win them all, right? Your goal is to put yourself into position to win the LAST point. Translated, that means you have to put yourself in position to answer the last question - you have to have time to address it. Otherwise, you've lost the last point, and by extension the match. When the other guy hits a winner, don't go running after it so fast that you hit the fence and injure yourself, thereby hurting your chances on the later points. (Translation: don't go way over when the problem is too hard.)
I'm having hard time increasing my speed with accuracy.
You do not need to maintain that 80% accuracy (on the ones which you actually answer). You only need about 60% accuracy, and you need that accuracy to be steady - not a higher accuracy until you run out of time and then a bunch of incorrect questions in a row. You need to increase your speed and sacrifice your accuracy!
First, go read our free e-book The GMAT Uncovered. It's in your student center. Pay particular attention to the scoring section - if you understand how the scoring actually works, then that will make it easier for you to make better decisions about how you are spending your time.
Next, this article can help:
http://www.beatthegmat.com/mba/2009/12/ ... managementI think you would also benefit from a timing exercise: learning about how long one minute is without looking at a watch or stopwatch. If you don't have one already, buy yourself a stopwatch with lap timing capability. When you go to do a set of problems, start the stopwatch but turn it over so you can't see the time. Every time you think you're one minute into a new problem, push the lap button. When you're done with that problem, push the lap button again, then repeat the process for the next problem. When you're done with the set, see how good you were - and whether you tend to over or underestimate. Get yourself to the point where you're within 15 seconds either way on a regular basis (that is, you can generally predict between 45 sec and 1min 15 sec). Also check your timing for the entire question, of course.
Now, how do you use that when doing problems? If you're not on track by one minute*, make an educated guess** and move on. (The general idea is that if you're not on track by the halfway mark, you're unlikely to figure out what's holding you back AND have time to do the whole problem in the 1 min you have left.)
* For SC, 1min is well beyond the half-way mark (we're supposed to average about 1m15s here), but you can almost always eliminate at least some choices on SC in that timeframe. Once you've got that "I'm around the 1min mark and I'm struggling" feeling, go through any remaining choices ONCE more. Pick one. Move on.
** This also requires you to know HOW to make an educated guess depending upon the type of problem and the content being tested. So that's something else to add to your study: how to make educated guesses on different kinds of problems.
For CR, try these articles for additional ideas / help:
http://www.manhattangmat.com/articles/C ... n-type.cfmhttp://www.manhattangmat.com/articles/CR-assumption.cfmhttp://www.beatthegmat.com/mba/2010/01/ ... cr-problemhttp://www.beatthegmat.com/mba/2009/10/ ... -questionsFor RC:
http://www.beatthegmat.com/mba/2010/04/ ... mp-passagehttp://www.beatthegmat.com/mba/2010/07/ ... rc-passagehttp://www.manhattangmat.com/articles/a ... estion.cfmhttp://www.beatthegmat.com/mba/2010/11/ ... il-problemBut timing is your major concern right now - if you don't fix that, your score isn't going to lift much. Start there!