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 my honorable experts GMATNinja, MartyMurray, VeritasPrepBrian, AjiteshArun, VeritasKarishma
This is just for curiosity--->
Is there any chance to add another possible correct choice for this CR?
Thanks__

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__

Sure. We can come up with any number of weaken options for this (or any other) question. But why would we? There can be at most only one correct option in any GMAT CR question
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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!

The guidebook writer will take E as evidence for HIS point!! So, E is definitely wrong way.
Thanks__

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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Hi GMATNinja, Now it's clear to me. Thanks for your cordial response though it's a bit late!

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....

You are looking for extreme cases to support the incorrect option and weaken the correct option. This is not what CR, or verbal in general, is about. We need to mark the best answer out of the 5 options given to us. The correct option is probably not going to be "watertight".

As for E, it is completely counter-intuitive to think that spending significantly less time as an apprentice can somehow lead to better training/learning. Sure, maybe a few carpenters who turn out to be geniuses don't need as much time learning from someone else, but are we willing to say that (on average) carpenters have started benefiting from spending significantly less time learning?

Learn from questions like this one, but the fact that you can take different things out of the options you encounter tells us that you are able to look at statements from multiple angles. That ability could hurt your score, however, if you give too much importance to extremely unlikely scenarios. Practice sticking to the most likely interpretation instead.
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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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GMATNinja - Excellent explanation as usual...
Thank you !!

Posted from my mobile device

Hi generis
What if?
If 1930 is replaced with 2019 in the argument? Will the choice D still be correct choice?
Thanks__

Guidebook writer: I have visited hotels throughout the country and have noticed that in those built before 1930 the quality of the original carpentry work is generally superior to that in hotels built afterward. Clearly carpenters working on hotels before 1930 typically worked with more skill, care, and effort than carpenters who have worked on hotels built subsequently.

Which of the following, if true, most seriously weakens the guidebook writer’s argument?

Pre-thinking
The author reasoning is that carpenter working on hotels before 1930 were more qualified, skilled... and after 1930 they were not anymore.
A way in which we could weaken the argument is suggesting another reason for the change in the hotels after 1930. For example the owner wanted to build hotels faster and cheaper so even if carpenters had the same working abilities as before under these new working conditions their work would be of a lesser quality.


(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.
This choice talks about entities that are out of the scope of the argument. Hence incorrect.

(B) Hotels built since 1930 can generally accommodate more guests than those built before 1930.
This choice does not clearly affect the argument since it does not say how this could impact the quality of carpenters work. Let's say that before 1930 hotels could accommodate only 100 people with 20 rooms and the ones built after 1930 could accommodate120 people with 24 rooms. in this case the quality of the work of carpenters should not be impacted by the higher occupancy. Hence incorrect

(C) The materials available to carpenters working before 1930 were not significantly different in quality from the materials available to carpenters working after 1930.
This strengthen the conclusion since it eliminates an option that could have suggested another possible reason for the decrease in quality. Hence incorrect

(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 option suggests that the quality of the carpentry is a significant factor affecting the quality of the building. This option leaves scope for suggesting that the actual reason for the decrease in quality in hotels built after 1930 is due to the quality of carpentry. Hence correct

(E) The average length of apprenticeship for carpenters has declined significantly since 1930.
This strengthen the conclusion. Hence incorrect

Thinking: to me D is a very subtle answer. I would assume this rule holds true towards buildings both built before 1930 and after (e.g. 1935), meaning all bad buildings will be demolished and good quality ones stick around. So it doesn't weaken the argument that much.

2nd thought to A: the average lifespan for buildings before 1930 is still longer than that of after, so a bigger portion of buildings got a chance to be obsoleted and demolished, leaving a bigger proportion of quality buildings

And since all other 4 answers are definitely strengthen, even though D is subtle one you should go for it.

Dear Friends,

Here is the detailed explanation to this question-




Mind-map: Pre-1930 hotels had better carpentry→ pre-1930s carpenters had more skill

Missing link: Between high quality pre-1930 hotel carpentry and conclusion that pre-1930 carpenters had more skill.

Expectation from the correct answer choice: To undermine link between high quality pre-1930 hotel carpentry and conclusion that pre-1930 carpenters had more skill.

Choice A: This answer choice is irrelevant, as it makes a comparison between the quality of carpentry in hotels and other structures such as houses and stores, without referring to the link between high quality pre-1930 hotel carpentry and the conclusion that pre-1930 carpenters had more skill at all; therefore, it is an incorrect answer choice.
Choice B: This answer choice fails to address the link between high quality pre-1930 hotel carpentry and the conclusion that pre-1930 hotel carpenters had more skill, as it remarks on the building style of post-1930 hotels alone, without making any reference to the quality of carpentry employed therein. Furthermore, the fact that hotels post-1930 are built to accommodate more guests has no bearing on the quality of the carpentry employed therein; both these paths of reasoning demonstrate that this answer choice does not fulfil the expectation from the correct answer choice, making it an incorrect answer choice.
Choice C: This answer choice establishes that carpenters working on hotels both before and after 1930 had access to building materials of similar quality; therefore, it becomes clear that differences in the quality of carpentry in hotels before and after 1930 cannot be attributed to a significant difference in the quality of materials used in the respective periods, thereby removing a possible alternative explanation for the observations made by the guidebook writer; it is, therefore, an incorrect answer choice.
Choice D: This answer choice states that if buildings employ higher quality carpentry while being built, they are likelier to maintain their utility into the present day; accordingly, pre-1930 hotels with lower quality carpentry are unlikely to survive into the present day, while those with higher quality carpentry are likelier to survive, thereby offering an alternative explanation for the increased presence of higher quality carpentry observed by the guidebook writer in pre-1930s hotels, as compared to a lack of such consistently high-quality carpentry in more recent hotels; one can reasonably conclude that more pre-1930s hotels have highly skilled carpentry work because hotels from the same period with lower quality carpentry probably fell into disuse; this undermines the direct link between high-quality pre-1930 hotel carpentry and the conclusion that pre-1930 carpenters worked on hotels more skilfully and is, therefore, the correct answer choice.
Choice E: This answer choice states that apprenticeship durations have decreased since the 1930s, implying that carpenters who have taken up the trade since have spent less time on training themselves than did their pre-1930s predecessors, leading to a decline in the general skill level amongst carpenters post-1930s; this argument is in accordance with the argument advanced by the guidebook writer as it strengthens the link between high quality pre-1930 hotel carpentry and the conclusion that pre-1930 carpenters had more skill, and is, therefore, an incorrect answer choice.

Hence, D is the best answer choice.

To understand the concept of “Characteristics of a Weakening Statement on GMAT Critical Reasoning,” you may want to watch the following video (~3 minutes):



All the best!
Experts' Global Team
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Guys i have found very similar question, for which the answer is not matching with what we have here

https://gmatclub.com/forum/the-brochure ... 48969.html

can any body shed some light?

Thanks all for your answers. The one thing I don't understand here is the idea that a hotel having good carpentry meaning it won't be knocked down affecting pre-1930s hotels more than post-1930s hotels. Even if the likelihood of being knocked down when you have poor carpentry increases with age, (which is an assumption, not stated anywhere) then hotels built in 1931 would have marginally worse carpentry on average than hotels built in 1929.

I see why it may be the correct answer through elimination, but in my opinion is nonetheless a poor argument, and does very little to weaken the guidebook writer’s argument.

Guidebook finds the quality of hotels before 1930s far more superior than those built later. Then he quotes one of the possible conclusion for his explanation that carpenters worked with more effort and care etc. before 1930 than later.

Notice this is one of the possible conclusion not the only conclusion.

We want to weaken the conclusion then we can bring in the statement which decreases our belief in conclusion.

choice A: We are not comparing hotels with Houses etc.

Choice B: Irrelevant - hotel guests not linked with quality of hotel

Choice C: this actually strengthens the conclusion that even if the material available to the carpenters before 1930s and afterwards were the same, then still the quality before those of 1930s is far superior.

Choice D: This undermines the conclusion wherein we need infer further from this statement. If low quality building are demolished that implies the building from before 1930s that are left are only high quality. BUT what if there were in total 10 buildings befoe 1930 and 8 of those were of low quality and demolished and only 2 are still there. This doesn't let us generalize that quality in general was good.

Choice E: This kind of strengthens the conclusion that if carpenters before 1930s were given more apprenticeship then they were thus able to build high quality buildings.