Let's take another look at D.


So if the quality of original carpentry is lower in a building, then that building is more likely to fall into disuse. However, this choice does not say that a building with low quality carpentry will immediately fall into disuse upon being built.

Imagine that we build one group of buildings with low quality carpentry and, at the same exact time, another group of buildings with high quality carpentry:

• After 10 years, perhaps all of the buildings are still standing.
• After 20 years, perhaps 1 building from the low-quality group has fallen, while all of the buildings from the high-quality group still stand.
• With each passing decade, it becomes more and more likely that a building from the low-quality group will fall into disuse and be demolished.
• After a century, maybe a couple buildings from the high-quality group have been demolished, while most buildings in the low-quality group have been demolished.

Coming back to the argument, perhaps some of the low-quality, post-1930 hotels have already been demolished. But it is certainly possible that many of the newer low-quality hotels are still standing.

And when we consider a group of low-quality hotels built before 1930 vs. a group of low-quality hotels built after 1930, odds are that a higher percentage of the pre-1930 group has fallen into disuse over time. This would certainly skew the data observed by the writer.

As I've written earlier, we cannot PROVE that this is the case. But by providing an alternative explanation for the writer's observations, choice (D) certainly weakens the author's argument.


Here's choice (E) again:

Sure, no part of this choice tells us about the carpenters' amount of care and effort. But apprenticeship is where carpenters develop skills, and carpenters' skills are still part of the conclusion. So If the average length of post-1930 apprenticeships are shorter, then we're more inclined to accept the conclusion than reject it. This may not prove the conclusion, but it definitely doesn't weaken the conclusion. Without more information, (E) is more likely to strengthen the argument than weaken it.

This is why (D) creates much more doubt about the conclusion than (E). I hope this helps!
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Hi GMATNinja,
Thanks for your nice explanation. I'm happy with your extraordinary explanation, but I'm a bit confused about the highlightedpart that you wrote above.
Q: Is it necessary/mandatory to disprove the author's conclusion to weaken this types of CR questions?
Thanks__
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Actually, I tried to find out at least one possible correct choice other than official correct choice for this CR, but I am fail! So, could you help me to find out any possible correct choice?

For the highlighted part: In most of the assumption question, we can find many more possible correct choices, but I did not find any correct choice for this one!
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Absolutely not. That is my point -- choice (D) does not disprove the conclusion, but it certainly weakens the argument. And we were asked which choice most seriously weakens the argument, so (D) is a very attractive choice.

I hope this resolves your doubt!
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GMATNinja VeritasKarishma

Hi..I had a doubt regarding the following explanation provided by GMATNinja for choice (D):

"Choice (D) implies that buildings with low-quality carpentry are likely to fall into disuse and be demolished. So what about the low-quality hotels built before 1930? Well, if choice (D) is true, it is likely that those old, low-quality hotels have fallen into disuse and been demolished. If that's the case, most of the pre-1930s hotels that have NOT been demolished are likely to have HIGH-quality carpentry."
My confusion:

So to accept choice (D) as the weakener, we have to further assume that there were many hotels built in the pre-1930s which have subsequently been demolished thus proving that they were of low quality.But we cannot say for sure that this is true. May be all the pre-1930s hotels are still standing , thus proving that they were indeed better built than those of post-1930s...

Now analysing choice (E):
"The average length of apprenticeship for carpenters has declined significantly since 1930."

If this were true we can say that the carpenters of post-1930 era hasn't been equipped with the proper training as were those of the pre-1930s era...Indeed this could have been false...But as in (D) a small assumption in (E) that the shortening of the length of apprenticeship has led to the carpenters of the post-1930s not being as equipped in the craft as those of the pre-1930s negates the possibility that the carpenters of the previous generations worked with more skill and care than those of the later generations. Maybe it was just the extra knowledge acquired during the apprenticeship that had made all the difference.

Please explain where am I going wrong....

Conclusion: Clearly carpenters working on hotels before 1930 typically worked with more skill, care, and effort than carpenters who have worked on hotels built subsequently.

Analysis: Incomplete Information- The author failed to consider all of the possibilities.


(A) The quality of original carpentry in hotels is generally far superior to the quality of original carpentry in other structures, such as houses and stores.
out of scope
(B) Hotels built since 1930 can generally accommodate more guests than those built before 1930.out of scope

(C) The materials available to carpenters working before 1930 were not significantly different in quality from the materials available to carpenters working after 1930. Opposite: This one kind of supports the author's argument. Rules out one of the possibilities that materials used by the carpenters of two eras were different

(D) The better the quality of original carpentry in a building, the less likely that building is to fall into disuse and be demolished.This one gives another plausible explanation of the reason for the observation by the author

(E) The average length of apprenticeship for carpenters has declined significantly since 1930.Opposite: This one kind of supports the author's argument.
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Hi generis
What if?
If 1930 is replaced with 2019 in the argument? Will the choice D still be correct choice?
Thanks__
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