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## [720 Q49 V40] My Blog: Errors and lessons learned

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mayonnai5e GMAT Titan
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Fri Sep 14, 2007 4:03 pm
My general CR strategy:

I read the stimulus the first time around fairly quickly then summarize the stimulus in my mind and look at the answers. I eliminate the obvious incorrect choices and if there are 2 or more choices left, I go back to the stimulus and reread again, paying particular attention to small details like adjectives and other "qualifying" words.

For some easier CR questions, the answer will leap out at you so don't waste time super analyzing the stimulus before reading answer choices. Get a general idea then try to find the answer. This saves time in the long run. If, however, the answer is not immediately apparent, go back and look for the tiniest details because the subtle details often are the key to eliminating the remaining incorrect answer choices.

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mayonnai5e GMAT Titan
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Fri Sep 14, 2007 5:59 pm
Man, doing 30 timed, CRs in a row is exhausting. It doesn't help that it's 2:30 AM here in Paris either. But at least I've completed the CR section of the OG11 book. For the entire section, my hit rate was 89%. That's not as good as I had hoped, but I have to keep in mind that most of my progress made in CR actually came from doing these problems.

Anyways, one of the last problems in the book illustrates one of the lessons learned I mentioned earlier in this blog. The lesson I'm referring to suggests paying attention to premises and conclusions and clearly distinguishing between the two because some answer choices will discuss the premises instead of the conclusion. The idea is that the test taker will see a topic discussed in the stimulus and select that answer choice. The question I am referring to is #121 in OG11 page 503:

Quote:
Northern Air has dozens of flights daily into and out of Belleville Airport, which is highly congested. Northern Air depends for its success on economy and quick turnaround and consequently is planning to replace its large planes with Skybuses, the novel aerodynamic design of which is extremely fuel efficient. The Skybus' fuel efficiency results in both lower fuel costs and reduced time spent on refueling.

Which of the following, if true, could present the most serious disadvantage for Northern Air in replacing its large planes with Skybuses?

(A) The skybus would enable Northern Air to schedule direct flights to destinations that currently require stops for refueling.
(B) Aviation fuel is projected to decline in price over the next several years.
(C) The fuel efficiency of the Skybus would enable Northern Air to eliminate refueling at some of its destinations, but several mechanics would lose their jobs.
(D) None of Northern Air's competitors that use Belleville Airport are considering buying Skybuses.
(E) The aerodynamic design of the Skybus causes turbulence behind it when taking off that forces other planes on the runway to delay their takeoffs.
Several of the answer choices relate to fuel; in particular, A and C provide extra information about the new plane would affect fuel usage. Unwary test takers may see the abundance of answer choices regarding fueling and think one of those choices must be the answer. In addition, notice how fuel is the last thing discussed in the passage. But what is the purpose of the discussion of fuel? It is a premise!

"...is planning to replace its large planes with Skybuses, the novel aerodynamic design of which is extremely fuel efficient. The Skybus' fuel efficiency results in both lower fuel costs and reduced time spent on refueling."

The fuel efficiency and refueling time properties of the Skybus are part of the premises and must be true. The question asks you to present the most serious disadvantage. In order to do this, we need to find out what is crucial to the success of the company and that is mentioned just briefly:

"Northern Air depends for its success on economy and quick turnaround"

Some people would probably read this part quickly and not really absorb it's significance. Then, seeing how the rest of the stimulus focuses on the fuel aspects, would focus on the fuel related answer choices.

A and C both provide an advantage for the airline while D is irrelevant. The remaining choices are B and E. My initial guess was B since a decline in fuel price would appear to minimize one potential benefit of the Skybus: lower fuel costs. But after thinking it through, the sentence about the fuel cost benefits was a premise and must be assumed true so choice B cannot be the correct answer - there's no reason to weaken a premise. So the only choice left is E, which discusses how the new plane can slow other planes down including some of Northern Airs'.

You can refer to the OG explanation for another explanation, but this is how I approached the problem.

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Fri Sep 14, 2007 8:38 pm
:thumbsup:

'blogging' is lonely very lonely, at least at the starting phase... guess you have come out of that phase now...

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Please do not PM me, (not active anymore) contact Eric.

mayonnai5e GMAT Titan
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Sat Sep 15, 2007 4:12 pm
I've seen the SC problem several times, but have never been able to figure out what's wrong with one particular answer choice. Tonight, while I was doing a timed practice set from the OG SC set, I saw this problem again and finally figured out what the error is.

Quote:
The peaks of a mountain range, acting like rocks in a streambed, produce ripples in the air flowing over them; the resulting flow pattern, with crests and troughs that remain stationary although the air that forms them is moving rapidly, are known as "standing waves."

(A) crests and troughs that remain stationary although the air that forms them is moving rapidly, are
(B) crests and troughs that remain stationary although they are formed by rapidly moving air, are
(C) crests and troughs that remain stationary although the air that forms them is moving rapidly, is
(D) stationary crests and troughs although the air that forms them is moving rapidly, are
(E) stationary crests and troughs although they are formed by rapidly moving air, is
A, B, and D are clearly wrong because of the "are" at the end. However, the last two choices are similar and both appear to be correct in terms of verb tense and pronoun agreement, but E is wrong and C is the correct answer.

Why is C more correct than E? Because of the word although. Although signals a specific linguistic element - mainly that something occurred even though something that appears contrary to it is evident. For simplicity's sake, let's interchange although for the phrase "even though" because even though is more often used in spoken English:

"Harry Potter is a great wizard even though he is a young boy" (I just watched Harry Potter and the Order of the Phoenix =P).

Notice how the thing that is being contrasted (great wizard) occurs just before the even though in the sentence. Now let's change even though back to although:

"Harry Potter is a great wizard although he is a young boy"

Let's look at choice C:

(C) crests and troughs that remain stationary although the air that forms them is moving rapidly, is

What is being contrasted? The "stationary-ness" of the crests and troughs.

--> Harry Potter is a great wizard although
--> crests and troughs that remain stationary although

Now let's look at E:

(E) stationary crests and troughs although they are formed by rapidly moving air, is

Notice how what is being contrasted is far away from the although. It is actually a little bit unclear what is being contrasted.

Convert this to the Harry Potter analogy:

"The great wizard Harry potter although he is a boy"

Hmmm....this is far from clear. In fact, the use of the although in these last two sentences suggests something is coming up to clarify the contrast:

"stationary crests and troughs although they are formed by rapidly moving air, are slow and dormant"

"The great wizard Harry potter although he is a boy, is very tall."

Lesson: Make sure what is being compared/contrasted by "although" is clear and close to the word although*

*unless although is used at the beginning of the sentence ==> "Although Harry Potter is a young boy, he is a great wizard"

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mayonnai5e GMAT Titan
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Mon Sep 17, 2007 5:21 pm
Wow, it turns out that I'm terrible at DS under timed conditions. I just did questions 76-95 of the DS in OG11, which aren't even the hard problems, under timed conditions, and I did terribly! How bad? My hit rate untimed for questions 1-75 was roughly 93% and my hit rate tonight for this set was 75%.

Granted 1) I did this set at 1AM in the morning 2) got a total of 6 hours sleep last night and 3) worked 8 hours 4) studied permutation/combinations/probabilities for 2 hours and 5) these problems are noticeably more "tricky" than the previous 75, I'm still surprised by how many I got wrong. I stopped because it was too demotivating seeing so many errors. I noticed the time pressure forced me to move on without spending the extra seconds needed to ensure I covered all my bases. There were definitely things I simply overlooked and would have clearly seen had it not been for the time pressure.

I'll see how I fare on the next few sets, but this may be another weakness that I need to address (timed DS questions).

By the way, anyone have a similar experience and/or have advice on how to minimize this weakness?

Lesson of the day: don't do DS timed at 1 am in the morning off 6 hours sleep and after 8 hours of work and 2 hours of studying. =\

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Mon Sep 17, 2007 6:29 pm
I ran into a similar situation as you did during my GMATPrep--I found that I could go through PS questions much faster than DS questions.

My workaround for this situation was to train myself to go through PS questions under 1 minute, and DS questions under 2 minutes. By keeping this pace, I was able to complete the overall quant section in time.

Otherwise--the key to getting faster in DS is just simple practice. Understand the concepts well and apply them over and over again, and you'll speed up your pace...

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mayonnai5e GMAT Titan
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Tue Sep 18, 2007 1:23 am
beatthegmat wrote:
Otherwise--the key to getting faster in DS is just simple practice. Understand the concepts well and apply them over and over again, and you'll speed up your pace...
Agreed. I hadn't done any DS questions in over a week and that may have affected my accuracy and speed as well.

mayonnai5e GMAT Titan
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Tue Sep 18, 2007 8:02 am
I've taken a lot of good lessons learned in the past few days and will post some soon...

mayonnai5e GMAT Titan
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Tue Sep 18, 2007 10:38 am
Some important properties of 0:

--> 0 * 0 = 0
when? DS
context? xy = 0; xy >=0; xy <=0
why? unless stem states x, y are non-zero either or both can be 0

--> |0| = 0
when? DS
context? |x| used in anyway (e.g. |x-3| > y, |xy| = c)
why? special case that can be a trap

--> (0)^2 = 0
same as |0|...see above

--> 0 is non-negative
when? PS/DS
context? N is the set of first 15 non-negative integers, x and y are non-negative integers...
why? don't forget to include 0 in sets/ranges/values/etc

--> 0 is non-positive
same as above

--> 0/y = 0
when? DS/some PS
context? x/y >=0
why? 0 divided by anything is 0 so any division that does not exclude 0 as a possible value for the numerator can have 0 as the numerator

--> sq. root(0) = 0 since 0^2 = 0
when? DS
context? if sq root(x) = y, what is y?
why? may forget to leave out a possible value for x

There may be others that I've forgotten to include.

mayonnai5e GMAT Titan
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Tue Sep 18, 2007 10:59 am
Dealing with divisors, factors and multiples:

Remember they are all different sides of the same coin (if a coin had 3 sides). What do I mean?

If X is a divsor of Y, then X is a factor of Y
4 is a divisor of 8, 4 is also a factor of 8

If X is a multiple of Y, then X is divisible by Y
4 is a multiple of 2, 4 is divisible by 2

If X is a factor of Y, then Y is divisible by X and Y is a multiple of X
4 is a factor of 8, 8 is divisible by 4, 8 is a multiple of 4

If X is divisible by Y, then X is a multiple of Y and Y is a factor of X
4 is divisible by 2, 4 is a multiple of 2 and 2 is a factor of 4

If X is a multiple of Y, then X is divisible by Y, Y is a divisor of X, and Y is a factor of X
4 is a multiple of 2, 4 is divisible by 2, 2 is a divisor of 4 and 2 is a factor of 4

If the above seems confusing, pick a few numbers and write out their prime factorizations in a tree format and stare at them for awhile. Verify the things I've said above and see how the tree describes the relationship between the three.

Remember: Multiples are at the root (top of the tree), divisors and factors are on the bottom of the tree.

Post reply or PM if this needs further explanation.

mayonnai5e GMAT Titan
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Tue Sep 18, 2007 4:41 pm
DS. Sucks.

I finished the rest of the DS problems in the OG book and found my hit rate plummeted with the harder questions and under timed conditions. (57.5% on the last 40 questions timed). I've made a post in the MATH DS forums for suggestions/ideas on how to specifically improve this area of Q. Please reply on that thread if you have any suggestions.

http://www.beatthegmat.com/viewtopic.php?p=20991#20991

On the bright side, I actually noticed some lessons learned while doing the test. I found faster ways of doing specific problems. Hopefully the solutions will be very good and help a lot.

People on this forum have mentioned that the OG math questions are not that difficult (600-700) range so it's kind of demoralizing to see that my hit rate so low. I guess I'll just have to offset that by getting 100% of the PS questions correct. =P.

On bright side: 57.5% means huge room for improvement.

Wed Sep 19, 2007 4:54 pm
Hang in there man! You have a great approach to your studies, I'm sure you'll be improving your DS.

mayonnai5e GMAT Titan
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Fri Sep 21, 2007 12:55 am
Anonymous wrote:
Hang in there man! You have a great approach to your studies, I'm sure you'll be improving your DS.
Thanks for the support. I'm trying!

mayonnai5e GMAT Titan
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Fri Sep 21, 2007 2:07 am
I haven't done any practice problems in the past two days. I finished up the DS section on Tuesday (last 60 problems) and did poorly on them so I've shifted my focus from completing the OG to focusing on lessons learned from the DS section. To that end, I've been slowly and methodically going over every solution. My approach:

1) Before looking at the solution, go through the problem again mentally and look at my practice work to see how I did the problem
2) Note any approaches that seem overly computational or require a lot of plugging in/picking numbers
4) Note any shortcuts or insights provided by the explanation that I overlooked or did not see.
5) Write down lesson learned on how I can see that shortcut or insight next time I see a problem with similar characteristics.

At the rate that I've been going, I can only cover 20 problems in 2 hours, which is 6 minutes per question on average.

As mentioned in this blog before, quality over quantity. Quality is where you learn the most.

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Fri Sep 21, 2007 6:53 am
mayonnai5e - the link to your blog doesn't seem to be working for me..... is it still up and running or have you taken it down? thanks

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