Data Sufficiency

ok up to here:

psm12se wrote:4. so from this we can see that line 'B' and the reflected line of 'A' are not parallel as they don't confirm to the formula m1*m2 = -1

that's the formula for perpendicular, not parallel.
(if you think about it for a sec, it should be obvious that this can't be the formula for parallel. if the product is -1, then one slope is positive and the other is negative -- definitely not parallel!)

parallel lines have the same slope.

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if the question said "perpendicular" where it currently says parallel, then the answer would *not* be (e), since in that case you would never get a "yes" answer.

ngalinh wrote:ultimately, it's great to know the initial thought or set of questions that leads to a finding of a method or a solution.

well, if you are totally stumped by a problem when you first see it, then, yes, you should look for "signals" or "clues" when you review it.

on the other hand, don't forget that the end goal here is to develop an intuition for solving the problems.
i.e., you can think about explicit signals when you are first learning how to do something, or when you haven't really mastered a topic yet. but, over time, the goal is to move away from having to think explicitly about "i see this, that means i should do this", and to move toward seamless recognition/intuitive thinking.
that's the one thing that you have to get from practice. even "super gmatters", as you call them, don't see all of these things from the beginning.

(for example, when I listened to your lecture about parallelism, you said: we should count the list from left to right.

right to left, maybe?
(left to right is the normal order, so that wouldn't be much of a revelation for anyone.)

I thought, how could he come up with such amazing thing?

i think you're giving me too much credit here.

in the particular case you're talking about, i just did these things:
1/ look at the sentence
2/ note that it's impossible to determine the parallel structures from left to right
3/ say, "oh well"
4/ go from right to left, since, well, that's the only other thing that's possible.

i don't know the specific example, but here's a pair of sentences, both of which are parallel:
This animal lives in grass and trees.
This animal lives in grass and in trees.

now, here are the same sentences with the parallel structures highlighted:
This animal lives in grass and trees.
This animal lives in grass and in trees.

the right to left thing is far from genuis here. it's just a result of two observations, both of which are pretty clear if you're thinking about them:
1/ the parallel structures can't be determined from left to right. (both sentences start with exactly the same words, but the parallel structures are different.)
2/ the only signal of the parallel structure is "and" -- which you don't see until you're looking at the second half of the parallelism (the trees part). once you see that, you think, "whoa! this is the second half of some parallel thing", and then you go back and find the first part.

ngalinh wrote:but maybe I have to clear the way (blocked by weaknesses) for intuition first?
for example, I don't totally understand many CR questions in 2mins or so, I mean I can't visualize the whole pictures with scopes limited by the conditions in questions. (the reason can be vocabulary, can be concepts, can be psychological problem: my brain automatically stop thinking when it sees new words- to preserve energy, I guess-so smart!) In this case, I can't expect to see intuitive thinking, can I?

the most important thing to realize here is that "intuition" is not some thing that superheroes have. basically, "intuition" is just a fancy-sounding word for "experiences you've actually bothered to notice and remember" -- either consciously or not, mostly unconsciously after a while. but, it goes without saying that you FIRST have to notice stuff with your conscious mind.
that may sound dumb, but remember that lots and lots of people just run through entire books trying to solve things, and don't pay much, if any, attention, to noticing things about the problems.

the worst approach here -- which, unfortunately, is also very common -- is to "review" by simply using exactly the same solution method again.
that kind of review is worth precisely nothing at all; it's just going around in circles. the way you build intuition is to look really hard (during review) for things you didn't see, or methods/tactics you didn't think of using, during the first go.

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ngalinh wrote:my brain automatically stop thinking when it sees new words- to preserve energy, I guess-so smart!) In this case, I can't expect to see intuitive thinking, can I?

in terms of "new words", i'll assume you're talking about the verbal section. (the vocabulary in the math section is extremely limited, so it's unlikely that you'll see any genuinely new words there. instead, the issue is that the language is unusually precise.)

the GMAT isn't meant to be a vocabulary-dependent test (as contrasted with, e.g., the GRE, which not only depends heavily on vocabulary, but also tests it directly). so, while "new words" are not a complete non-issue, they shouldn't have a ton of impact on your score, once you get past the remedial level of learning the english language. (from the way you write, it's clear that you are already past that level.)

in RC passages -- especially passages about law or science -- you're bound to see terms you don't really know. but, that's actually the point of including such passages: you're not even supposed to understand all the details in the RC passages.
see, that kind of reading -- reading in which you don't necessarily understand all the particulars, but you can nonetheless figure out the main themes/ideas -- is managerial reading, and this is a test for future managers.
if you're a manager at Apple and someone drops a 60-page white-paper about touch-screen components on your desk, you aren't going to read through all of the technical stuff. (at least i hope you aren't.) instead, you'll delegate that task to your engineering department, and instead ask the key questions, like "What does this mean for the user?" "What does it mean for our marketing?" etc.

for instance, if you have OG12, open that up to page 360 (a passage about dinosaur bones in the la brea tar pits).
ok, so, i got an 800 on this thing -- but i don't have clue #1 what "demographic bias" is. or what "local bias" is. or what "preservational bias" is.
i could probably figure out a rough idea, based on context -- for instance, it's pretty obvious that "local bias" refers to some sort of data distortion caused by not looking in enough different locations -- but that's not the point.
the point is for you to see those three kinds of "bias" and just think: Hmm... these are three possible objections, but the researchers ruled them all out.
that's it!
you can replace "preservational bias" with "pink flamingo", with zero adverse effects on this understanding.


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in CR, on the other hand, it's more possible -- not super-likely, but at least more possible -- that there will be some key vocabulary word that gives the passage a particular meaning. (i don't have any examples off the top of my head, but i've seen it happen.)
if that happens, then you just have to say "oh well", learn that word, and ... move on. (and, remember, it's an adaptive test, so it's ok to get lots and lots of stuff wrong.)

ngalinh wrote:my brain automatically stop thinking when it sees new words- to preserve energy, I guess-so smart!) In this case, I can't expect to see intuitive thinking, can I?

by the way, in response to your last question, i'd argue that seeing unfamiliar-looking words is one of the most intuition-intensive experiences out there.
after all, if you don't know what a word means, but you still want to understand what's happening in the area where that word appears, then you have to rely on ... intuition.
experience.
that thing. a sense of what is happening with the rest of the words. then, it's like having a jigsaw puzzle with one missing piece -- in 99.99% of cases, you can figure out exactly what's on that piece. in RC, you'll have enough context so that the same should be true.

lastly, notice the word "want" (boldface, above). that word is not an accident.
in fact, that's the single biggest predictor of whether you'll do well at RC and CR -- whether you can get personally involved in the situation(s) described.
if it's a CR problem about business, then, if you can get to the point of thinking that it's your business, then it will usually be very straightforward to solve the problem (regardless of ostensible difficulty level). if it's an RC passage, if you can become genuinely interested in what's stated, then you should find it easier to answer the questions.

yes, "becoming genuinely interested" here is ... not an easy thing. (who cares about 1960's feminist legislation, or about late-19th-century native land claims cases? not me, that's for sure.)
for me, I just imagine that I'm editing an article (which is cheating, of course, since I'm a professional editor). or else i'll imagine that the stuff described in the passage is what a friend does for a living and/or is interested in. but, any sort of personal involvement helps.

the same is true for math problems, too.
for instance, ok, i have this student who really likes shopping.
when i gave him "x is decreased by 40%, and the result is then decreased by 20%", he just couldn't wrap his head around the idea that the overall decrease wasn't 60%.
but then, i gave it to him as, "hey, Saks is having a sale. the stuff that's already marked down 40%, you get an extra 20% off the sale price." and, whoa! it's regular price x 0.6 x 0.8. he did it even faster than i'd do it.
... so, you see the point here: it's not even the objective material that's the issue (unless you actually lack the remedial foundation). instead, it's the fact that you're thinking about "x" instead of "something I want at Saks", and about "the result" instead of "the sale price on the tag".
yeah.
it's not the stuff; it's how you look at the stuff.

this is also the biggest reason why i got a really good score on the gmat exam. not so much because i'm "smarter" than anyone else (believe me, i am pretty dumb/dense in lots of ways)... but because i'm a huge nerd and i actually like solving random problems.

psm12se wrote:Thanks Ron for correcting me on step 4.

by mistake I wrote the slope of perpendicular line formula.

these things, they happen.

get up, dust yourself off, move on, and ... make sure it doesn't happen next time.