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Sampling in Official GMAT CR Questions

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Re: Sampling in Official GMAT CR Questions [#permalink] New post 15 Sep 2013, 20:48
Expert's post
egmat wrote:
bagdbmba wrote:
egmat wrote:
So, now if we consider period from 1600 onwards, the same logic will apply as the logic applied in case of 100 years and 1800 A.D.

The more you increase the average life, the more back in the time we'll need to go because in case of higher average life, we'll have more older hotels still in existence.


Hi Chiranjeev,
Thanks for the analysis.+1

I got your analogy clearly but still having some confusion on the above part...it seems to me that we're here applying some hard fast rule in order to make option D write.

The better the quality of original carpentry in a building, the less likely that building is to fall into disuse and be demolished. - how does it say something like in your analogy only those books of X are preserved now which were his best and the rest of the books were actually discarded...NOT able to relate these two parts.

Option D could also mean that most of the pre-1930 hotels exist today because of having superior quality of original carpentry...!

Please help. I'm really having a difficult shot to understand it.


Ok. Let me use some numbers here.

Suppose there are 1000 hotels that were created before 1930 and 1000 hotels that were created after 1930.

For the hotels created before 1930,

A1:Quality of 300 hotels = 100
A2: Quality of 400 hotels = 200
A3: Quality of 300 hotels = 300

Average quality = 200

For the hotels created after 1930,

B1: Quality of 300 hotels = 100
B2: Quality of 400 hotels = 200
B3: Quality of 300 hotels = 300

Average quality = 200

So, average quality for hotels from both period is same.

Now, let's bring option D into the picture.

The better the quality of original carpentry in a building, the less likely that building is to fall into disuse and be demolished

Now, tell me of hotels created before 1930, which hotels are more likely to exist now. A3? Right. After that? A2?

So, now let's suppose currently we have the following pre-1930 hotels left

A1: 150 (half of them got demolished)
A2: 300 (25% of them got demolished)
A3: 300 (None of them got demolished)

Average quality now = 2.2

For hotels built after 1930

B1: 240 (20% of them got demolished) (Since these hotels are built after 1930 and are newer than those built before 1930, the ratio of hotels that got demolished will be lower)
B2: 360 (10% of them got demolished)
B3: 300 (None of them got demolished)

Average quality now: 2.06

So, even though initial quality is same, because of option D, you see final quality of pre-1930 better than post-1930 hotels.

Just to emphasize, I did not chose these number to make option D correct; I chose them out of logic.

Let me know if it addresses your doubts.

Thanks,
Chiranjeev


Hi Chiranjeev,
Thanks for your further clarification.

So,here the caveat is NOT ALL the pre-1930 hotels are of same quality. Right?

If we presume this then only the above logic logic holds I think. Let me know whether I got it right?

And can you please share some hard OG questions on this concept? It'd have been much helpful then to implement the logic and understand whether it's clear! :)
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Re: Sampling in Official GMAT CR Questions [#permalink] New post 15 Sep 2013, 21:13
Expert's post
bagdbmba wrote:

Hi Chiranjeev,
Thanks for your further clarification.

So,here the caveat is NOT ALL the pre-1930 hotels are of same quality. Right?

If we presume this then only the above logic logic holds I think. Let me know whether I got it right?


Right. You need to presume this. Look at option D - it won't make any sense at all if all pre-1930 hotels were of the same quality. Option D makes it very clear that you need to presume this.

bagdbmba wrote:
And can you please share some hard OG questions on this concept? It'd have been much helpful then to implement the logic and understand whether it's clear! :)


The OG questions are listed within the article and the exercise questions of the article. I don't have any other questions handy.

Also, coming back to our question, option D says that as you go back in time i.e. as you look at more and more older hotels, you'll look at only the best of the best hotels because only those hotels would exist today. So, if you compare hotels built in 1800s with hotels built in last year, then you'll probably see a very huge difference in quality - you'll see that the average original quality of carpentry of hotels of 1800s is much more superior to the average quality today. This will be because most the lesser quality hotels of 1800s would not exist now while most best quality hotels would, as per option D.

Thanks,
Chiranjeev
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Re: Sampling in Official GMAT CR Questions [#permalink] New post 15 Sep 2013, 21:21
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Thanks Sir! :)

Looking forward to some more 700+ questions on this article in due course...
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Re: Sampling in Official GMAT CR Questions [#permalink] New post 15 Oct 2013, 21:56
can someone please explain the solution to this group wrt the sampling analysis
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Re: Sampling in Official GMAT CR Questions [#permalink] New post 15 Oct 2013, 22:35
nexuscrusher123 wrote:
can someone please explain the solution to this group wrt the sampling analysis



Please refer to the link motorcycle-safety-courses-offered-by-161004.html
This question is already discussed here. Nevertheless good question I fell for trap :s
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Re: Sampling in Official GMAT CR Questions [#permalink] New post 16 Oct 2013, 08:15
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abhinav11 wrote:
nexuscrusher123 wrote:
can someone please explain the solution to this group wrt the sampling analysis



Please refer to the link motorcycle-safety-courses-offered-by-161004.html
This question is already discussed here. Nevertheless good question I fell for trap :s


Thanks Abhinav for sharing the link.

Nexuscrusher123,

Please let me know if you still have doubts after going the thread mentioned by Abhinav.

-Chiranjeev
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Re: Sampling in Official GMAT CR Questions [#permalink] New post 19 Oct 2013, 21:11
thank you Abhinav and Chiranjeev.

please let me know if my thinking of the problem is on the right lines --

if significant percent of the population is trained (say 90%) then the sample and the population percentages are not similar. hence the argument here is weakened and it does not support the position taken about motor cyclists taking the course.
however if only around 8 percent of population has taken the course, then the sample and the population percentages are similar and it does support the position about motor cyclists taking the course.

does that sound about right?
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Re: Sampling in Official GMAT CR Questions [#permalink] New post 27 May 2014, 02:12
1 : C - it provide the that the data is representative

2. E - its' wrong sample

Thanks a lot e-GMAT for this very helpful article.
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Re: Sampling in Official GMAT CR Questions [#permalink] New post 09 Jul 2014, 12:31
knightofdelta wrote:
Very interesting stuff.

Answers

Question 1: C. X-rays of patients of many different orthopedists working in several hospitals were reviewed.

Option C will strengthen the argument because because the different samples of patients taken from many different orthopedists will cover a very wide range of the population covering both patients and doctors. This will reduce the bias towards a particular set of the population and thus make the argument stronger

Question 2:

E. Gold was not added to the soil samples collected by Frobisher before the samples were examined.
The argument states that the methods used to determine the gold content of Frobisher's samples must have been inaccurate. If the methods were indeed inaccurate, it means that the soil was not tampered with, that was why the the gold content of Frobisher's samples were high. By negating the statement and saying that Gold was added to the soil samples collected by Frobisher before the samples were examined, the argument breaks down completely because if Gold was added to the sample, it means that the methods used to determine the gold content of Frobisher's samples must have been accurate.



Hi,
I understand that for Q2 ,option E is correct .But I am not able to justify why option D is incorrect. On negating both seems to destroy the argument.
Can you please explain me why D is incorrect for Q2.
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Re: Sampling in Official GMAT CR Questions [#permalink] New post 09 Jul 2014, 13:02
Amazing explanation e-gmat.Would be great if we can have all the links together for the topics you discuss. :-D
Re: Sampling in Official GMAT CR Questions   [#permalink] 09 Jul 2014, 13:02
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