eliminating "Too Obvious" DS Answers

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by parallel_chase » Wed Aug 06, 2008 7:53 pm
Well I dont think your strategy of normal test taker will work for everyone on GMAT. How do you determine what a normal test taker would pick.

And more importantly how do you determine weather the question is hard or not?

Well you can start to see hard question from Ques#2 and rest depends on how well you do.
Source: — Data Sufficiency |

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by lunarpower » Wed Aug 06, 2008 11:53 pm
actually, yes, there's a quite potent strategy based on this idea: the strategy of eliminating the "c trap".

a c trap is a problem that's clearly written to be difficult, but on which both statements taken together are VERY CLEARLY sufficient.
and by VERY CLEARLY i don't mean "after i solve this equation, and move that over there, then ... oh yeah, my memorized rule of thumb tells me they're sufficient" - i mean it's OBVIOUS. (examples follow, for those of you who have your og's handy.)
on these problems, you can rest assured that (c) is not the answer. also, because the two statements together are sufficient, you can also strike answer (e).
this leaves only (a), (b), (d). and in the dream situation, in which one of the answers by itself is clearly insufficient, then you can guess that the other one must be sufficient - and you'll be right a startlingly high percentage of the time.

you should NOT use the "c trap" approach as a PRIMARY method - i'm sure that, one fine day, a difficult "c trap" problem will come along to which the answer actually is 'c' (although i've yet to see one) - but, rather, as an AID TO GUESSING.
still, if you get into a guessing situation, the c trap is one of the strongest weapons in your arsenal.

--

i'll illustrate two c traps from the og 11th edition (yellow book). i won't write out the problems themselves - don't want to step on any copyright toes - so, class, please get out your og11's and follow along.

DS PROBLEM 129:
* identify the problem as a c trap: if you take the two statements together, then you have values for ALL of the numbers in the problem (a, b, n). if you have specific values, then the answer will obviously be "yes" or "no"; hence, sufficient.
kill (c) and (e) and narrow the choices to (a), (b), and (d).

* statement (2) is clearly insufficient.
kill (b) and (d).

answer = a.

DS PROBLEM 150:
* identify the problem as a c trap: if you take the two statements together, then you have the prices of ALL the items in the problem. if that's the case, then the answer to the prompt question is clearly either "yes" or "no"; hence, sufficient.
kill (c) and (e) and narrow the choices to (a), (b), and (d).

* statement (2) is insufficient. this isn't nearly as obvious as it is for the aforementioned problem #129, but the presence of two remaining unknowns should convince you (remember that you're in guessing mode here).
kill (b) and (d).

answer = a.

--

class dismissed.
Ron has been teaching various standardized tests for 20 years.

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Re: eliminating "Too Obvious" DS Answers

by lunarpower » Thu Aug 07, 2008 12:05 am
shivf1 wrote:I am able to get most of the hard DS qns right using this technique...
you don't seriously mean "most", do you? if so, please post more details of the method you're using, as it will quite literally revolutionize the gmat preparation universe.
in my experience, the set of DS problems to which this sort of guessing method can be applied comprises a very small fraction of the overall DS pool.
shivf1 wrote:In REAL GMAT when will the harder DS qns start to appear?
In what qn range?
my guess is after qn numbers 25 or 28???
the test is adaptive, so the point(s) at which difficult questions will appear - as well as the point(s) at which they will cease to appear - is/are entirely a function of your ongoing performance on the test.
if you aren't getting the easy- or medium-difficulty questions correct, then the difficult questions won't show up at all.
if you nail the first few questions, then you will start seeing consistently difficult problems within at most the first 4-6 questions; the test adapts very quickly, so that it can mine your performance for as much meaningful data as possible.

from your question (#25-28) it seems that you don't realize the adaptive nature of the test; on one of the old-school paper tests, that's a decent estimate of the onset of "difficult" questions.
have you taken any practice tests from the last few years, and/or had exposure to the "adaptive" test algorithm?
Ron has been teaching various standardized tests for 20 years.

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