GMAT Ninja CR Ep 4: Obsessing Over Question Types

[@shreyasubramaniam4942]

The last one was a quant question that just forgot where it was going.

[@gutstodance9999]

the key things for the last question 1) focus on the number of copies 2) realize that the number of copies is directly related to the revenues; which make us choose between D and E; which is still freaking hard too do in a short amount of time !!! nice question !

[@prashantchandra5551]

Thanks to the GMAT Ninja team for compiling such comprehensive videos. Kuddos to Harry, Your explanations and teaching style have been the best among the lot.

[@GMATNinjaTutoring]

Thank you for the very kind words! I'm so pleased you've found the videos helpful. Best of luck with your GMAT studies, please keep us posted on how you get on!

[@Pb-gf2jw]

I am so impressed by the last question! Just blew my mind!

[@teslaecotech7076]

love you guys for putting up such high quality content here.

[@GMATNinjaTutoring]

Thank you! So glad you've found it helpful!

[@startcomplaining9781]

Question 3 is a tricky one, made me first think, that they confused revenue and net-income/profit. But as usual, they were right and I was wrong lol

[@jaesookna5201]

One of the best tutors 👍Thank you for your lecture

[@harryduthie]

Thank you for your very kind words, Jaesook! And best of luck with your GMAT studies!

[@utkarshsingh2675]

I think Q2 was quite a question....couldn't have come up with E as the answer tbh

[@bombaybarbell]

Got all the three questions right! But I really enjoyed the approach explained. Thank you, Harry!

[@GMATNinjaTutoring]

Thank you, Abhishek! I'm glad that you're enjoying these videos and making some progress. Have fun studying!

[@mayanksharma5114]

I am very new to GMAT preparation. I wholeheartedly agree with your assessment that categorising question into template is forcing a solution from a misunderstood problem statement. But, conversely does templating not cover most of the questions in GMAT(I don't know, I genuinely want to understand where to put my efforts into.). Does templating not improve speed even if it compromises on accuracy? I am not criticising, I really really wish to understand if templating (or things like reading the question before premise, or guessing the answers, or any other such quick hacks) is useful or not, and what my approach should develop as?

[@GMATNinjaTutoring]

Great questions! The problem with hacks such as reading the question first/guessing answers/templating questions is that they can cost you BOTH time and accuracy. For instance, if you try to anticipate the assumption for a certain argument, you might guess wrong and bias yourself against the ACTUAL right answer. What's the result? Sorting through the answer choices could take you even longer than it normally would, and on top of that, you might end up missing the question altogether. Templating and reading the question first can bias you in similar ways, so in the end, these techniques can do more harm than good. For more on our approach to CR and the logic behind our suggestions, feel free to check our Beginners Guide to CR at this link: www.gmatninja.com/gmat/articles/verbal/beginners-guide-to-gmat-critical-reasoning Let us know if that helps!

[@deveshbajpai8154]

​ @Harry Duthie Hi Harry .. thanks for the great work! Just one query regarding Question 2, was thrown off the right choice, as was in the habit of eliminating choices if they show an inversion of positive relationships or of negative relationships, for example, if X increases --> Y increases is part of the argument, would generally eliminate something implying X decreasing --> Y decreasing, by the reasoning that we don't know the inverse of the same relationship. Now, in the above, i understood the correlation causation reasoning, however still couldn't get over the fact that, on one hand, the argument states a positive relationship (more social interaction --> more mental sharpness), while on the other hand, the third-factor effect in the correct option uses a negative relationship (decrease in mental sharpness and decrease in social interaction ie. isolation because of medical conditions). Any suggestions on similar questions for practice and getting my mind wrapped around the concept?

[@harryduthie]

Hi DevT! Thank you for the great question! However, I don't know what you mean when you say "we don't know the inverse of the same relationship" as you're examining answer choice (E). The question says, "Which of the following, *if true* , most seriously weakens...", so we have to assume (E) is true in this question and examine how it affects the force of the evidence cited. I typically advise my students to avoid general rules about how to treat answer choices. These 'rules' can lead to the student making more mistakes in questions that present an exception to their rule, as this one did for you. It's great that you're noticing the differences between positive correlations and negative correlations in the passage and the answer choices, but you still have to consider whether that answer choice answers the question. I would never suggest crossing an answer choice out just *because* it shows the opposite relationship to the passage; I'd want to justify that reasoning first. I'm not 100% sure that's completely answered your question, but I hope it helps! Please let me know if you have any other questions and I'll do what I can to help.

[@deveshbajpai8154]

@@harryduthie The fact that you took some time out makes it a 110% satisfactory experience for me. Thanks for the great tip! I myself realized recently that there is no one rule, one has to evaluate and analyze then and there what the question requires us to do.

[@traviswilliams7746]

Hi Harry, I'm not sure if I'm misunderstanding something, but if the card is prepaid, as suggested by the passage, then why would revenues go up if it isn't fully used? Profits would go up, because they wouldn't be printing more pages, resulting in lower costs, but the revenue is generated at the sale. If you have the same number of copies as before, as suggested in the passage, and you have the possibility of even 1 person paying 1c less per copy, then your revenue would decrease, and D would be the closest answer. But even D has strong language in MOST, which I hesitate to select.

[@harryduthie]

Hi Travis, We can calculate the cost of the cards from the passage at $4.50 each (50 copies at 9 cents per copy). Answer choice then (E) tells us revenues will increase if these cards are "on average, used to significantly less than 90% of their capacity." If a card is used to exactly 90% of its capacity, the person who's bought that card will have paid $4.50 to make 45 copies. This is the same amount they would have paid if they hadn't bought the card and used the old system. If the card is used to less than 90% of its capacity, it will cost more per page to make copies using the new system than the old. We're told in the passage that the number of copies made in the library will remain essentially unchanged. *If* the cards that are bought are, on average, "used to significantly less than 90% of their capacity," then the people who bought these cards will be paying more per copy than they would have done under the old system and we can say that the revenue generated from photocopying will increase. This reasoning will also, hopefully, be helpful in eliminating (D). Revenues from photocopying will only decrease if the copy cards that are purchased are, on average, used to more than 90% of their capacity. Using the passage and (D) alone, there is no indication of whether the cards will be used this heavily, so we can eliminate (D). Just *because* an answer choice has strong language doesn't make it a good or bad answer; you've still got to think about the meaning of the whole answer choice. I hope that helps!

[@KaifBinArshad]

Understood,It is like Gym membership that if people pay $200/month then they use it for only that time when they go to gym but if one sells yearly membership for $2000 and people don't go to gym for more than a month then the gym will benefit from it.​@@harryduthie

[@grievousrationality4664]

Key concern with the last problem, how do we know the prepaid card is a one time use only card? Since when does prepaid card equate one time use?

[@GMATNinjaTutoring]

We don't get told that the prepaid card can only be used once, so it's probably safer to assume that the card can be used multiple times. The good news is that we don't have to worry about this since the explanation is the same whether the card can be used multiple times or only once. I hope that helps!

[@PARItosh6366]

Hi team really great content . I feel so much more confident while attempting CR questions now . Just one question, are question 2 and 3 650+ level questions ?

[@GMATNinjaTutoring]

That's great that you're feeling much more confident! Thank you for the kind words. Using the difficulty ratings on GMAT Club, which isn't perfect but gives us a good idea of how tough these questions are, both question 2 and question 3 are rated as 750+ level questions. I hope that helps!

[@vardanrathi7777]

In Strengthen Questions, we strengthen some specific part of the passage based on one of the 5 options. In questions which may seem like a strengthen questions but are not, we actually strengthen one of the 5 options based on the passage.

[@aartigupta0701]

In the second passage, for option C, can we say that as many ppl are good in both social interaction and in solving mathematical problem . The reason for mental sharpness was not due to social interaction rather because of math solving ability which weakens the evidence cited. What can be the reason for elimination: ? Is it because no where it is mentioned "ppl included in study". Can you please comment on that ?

[@GMATNinjaTutoring]

The evidence cited in the passage is a study showing a correlation between the social contact people report and the state of their mental skills. The correct answer will weaken the force of this evidence. Answer choice (C) tells us that many people are proficient at both social interactions and solving mathematical problems. There can still be a correlation between these two things, it's just a lot of people will be proficient at both. This answer choice doesn't "break" or weaken the correlation in the way answer choice (E) does. Further, (C) tells us about people's proficiency in solving mathematical problems which is not necessarily the same as their mental sharpness or mental skills. Solving mathematical problems is mentioned in the passage as one way people try to maintain their mental sharpness, but we can't say that solving mathematical problems is the same as someone's mental skills. This is an additional reason why we cannot say (C) weakens the force of evidence provided by the correlation. I hope that helps!

[@aartigupta0701]

@@GMATNinjaTutoring Got it now. Thank you so much!!

[@GMATTargetplus]

Hello Harry . Regarding Question 2 : We need to weaken the force of EVIDENCE. Now what is the evidence? Evidence is -A study showing that more the social contact people report , the better the mental skills. So , I was searching for an answer choice that provides some information about the study . Whereas the OA ie E doesnot attack the EVIDENCE. It says that social interaction doesnot lead to mental sharpness. Rather there is a third factor that affects both social interaction and mental sharpness. How does this impact the EVIDENCE ? Thanks.

[@harryduthie]

Hi Target 720plus, We don't necessarily need to attack the evidence, the correct answer choice only has to weaken the *force* of the evidence cited in the passage. The evidence provided is a study suggesting "the more social contact people report, the better their mental skills." In other words, there is a correlation between social contact and mental skills that the passage suggests provides evidence to support the claim that "simply talking to other people" is enough for people to "maintain mental sharpness as they age." (E) tells us that "many medical conditions that adversely affect a person's mental sharpness also tend to increase that person's social isolation." This provides a reason for the correlation: the people who have not suffered from one of these mental conditions will not have suffered from reduced social contact and reduced mental sharpness, while those who have will also have suffered the side effects of reduced social contact and mental sharpness. This means the study does not back up the claim made in the passage as strongly as before. (E) has reduced the *force* of the evidence, which is why (E) is the correct answer. One of your difficulties in this question might have come from how you say you were 'searching for an answer choice that provides some information about the study.' The correct answer *might* have done this, but it doesn't *need* to. I advise my students to stay away from trying to predict the correct answer as it can often end in situations like this where the correct answer isn't in the format you're looking for. All you can do is look at each answer choice and ask yourself if it answers the question. In this case, (E) does weaken the force of the evidence cited so even though it doesn't attack the evidence, it still is the correct answer to this question. I hope that helps!

[@nikkithashanker9386]

The 'also tends to social isolation' is confusing. If it was just "many medical conditions also adversely affect a person's mental sharpness despite good social skills" it somehow would have made more sense.

[@austinjon31]

You guys are doing awesome work!

[@harryduthie]

Thank you, Austin!

[@basharabuein409]

Hello! In the first question, why is A incorrect? The municipality would definitely want to buy a new system to replace their old one. QuickFreeze is a great replacement to the old one given that it is in some way an upgrade of the conventional system. So instead of just replacing the old one with the conventional system, they can hit two birds with one stone, and get the conventional one with the QuickFreeze upgrade.

[@GMATNinjaTutoring]

The passage tells us that the QuickFreeze system "works only when temperatures are cold," so any municipality buying a QuickFreeze system will "still need to maintain a conventional system." From this, we can tell that a municipality will have to buy a new conventional wastewater system if it has an old one that needs to be replaced. The QuickFreeze system cannot replace a conventional system, because it does not work when the temperatures are not cold. Answer choice (A) does not give us any grounds to say that a municipality will buy a QuickFreeze system IN ADDITION TO the conventional system it needs to buy to replace the old one. We don't have any reason to think the municipality will buy a QuickFreeze system just because it needs to replace its old system. However, if conventional systems are not full successful in killing bacteria at cold temperatures, then a municipality *would* have a reason to buy a QuickFreeze system IN ADDITION TO its conventional system. This is why (B) is the answer to this question. I hope that helps!

[@bennettko5026]

Can’t take the last few online lessons on CR before my exam😢 Still thank you for the excellent contents from GMATNinja!!

[@roysayantani]

The last question blew my mind :’)

[@aryan_0406]

Hi, I have 1 question regarding the structure of 2nd question. You said that it only contains information and no conclusion. But isn't a conclusion something which is supported by at least 1 premise. And in the argument it looks like the statement "In fact, however, simply talking to other people ... suffices" is supported by the evidence which shows more social contact, better mental skills. So, shouldn't this line "In fact, however, simply talking to other people ... suffices" be the conclusion of the argument?

[@GMATNinjaTutoring]

You're absolutely right: that's a conclusion and I should probably have been a bit more careful with the language I used at that point. The point I was trying to make in this explanation is that you'll run into trouble if you treat this question as a standard "premise-conclusion" passage and focus on the word "weaken" in the question. Really, all we need to focus on is the strength of the evidence provided by the final sentence of the passage. If we tried to find the answer choice that weakened the argument, as we might do if we skimmed the question and treated the passage as a standard GMAT 'argument' passage, we'd make it much more likely that we'd get the question wrong. If we treated the passage as if it was just providing information about a scenario and focused on the strength of the evidence given in the final sentence of the passage, we'd be acting more in line with what the question writers were looking for and we'd probably have a better chance of answering the question correctly. I hope all that makes sense and thank you for posting!

[@SwordSaint099]

Can someone please explain to me why the last question was E because at 31:55 he says that you pay $4.5 for 45 copies under the new system which isn't true since under the new system each copy only costs 9 cents which makes the total cost for 45 copies equal to 4.05.

[@GMATNinjaTutoring]

Under the new system, someone can buy a prepaid card for $4.50 which allows them to make 50 copies at 9 cents per copy. However, if this card is only used to 90 percent of its capacity, then that person will still have paid $4.50 for the card but they'll only make 45 copies. This means each copy will cost them 10 cents. It doesn't matter how many copies someone makes (as long as it's less than or equal to 50), they'll still pay $4.50 for the card. If the cards are used to significantly less than 90 percent of their capacity, then each person who buys a card will still have paid $4.50 for that card, but they will have made less than 45 copies. This means they will have paid more than 10 cents per copy for each copy they made, and this is how the library's revenue from photocopying rises if these cards are used "to significantly less than 90 percent of their capacity." I hope that helps!

[@USSCHANNEL]

In Question 3, i.e the library one, even in option E, I can argue that while on one card sold I may profit, number of people buying those cards may reduce. Hence there is no guarantee that overall revenue will increase. This is the reason I couldn't find even one correct answer here! Need help here.

[@GMATNinjaTutoring]

Everything you say in your first sentence is absolutely correct. However, I think your problems might start with what you say in your second sentence. Answer choice (E) doesn't say that overall revenue will increase. It says it will increase if certain things happen. That might seem like a small and inconsequential difference, but let's take a closer look at what's going on here. In the passage, we're told that the administrators think that the number of copies made in the library will not change after the refit. The question tells us to assume this assessment is correct, so we've got to assume the number of copies made will be the same before and after the refit as we examine the answer choices. Answer choice (E) suggests the library will see an increase in revenue from photocopying *IF* the people who buy copy cards use them "to significantly less than 90 percent of their capacity." If someone buys a copy card, it'll cost them $4.50. If they use 90 percent of the capacity, so they make 45 copies using the card, they'll have paid $0.10 per copy -- exactly the same as if they hadn't bought the copy card. If they use the card to less than 90 percent of its capacity, or they make less than 45 copies, the library will have increased its revenue per copy for that card. On the other hand, if someone makes a copy in the library without buying a copy card, the revenue the library receives per copy will be the same before and after the refit. So, we know the number of copies made in the library will be the same before and after the refit and we know that the library will increase its revenue per copy if the people who buy copy cards use them to less than 90 percent of their capacity. If we combine these two pieces of information, we can say that the overall revenue the library receives from photocopies will increase IF the people who buy copy cards use them to less than 90 percent of their capacity. This is why (E) is the correct answer to this question. I hope that helps!

[@omd3377]

Great video! Keep it up!!

[@GMATNinjaTutoring]

Thank you, and have fun studying!

[@q45dedos]

Thank you for the excellent content! :D

[@kanishksinghal2327]

In the second question, I don't understand how E weakens the evidence. As he clearly stated that social interaction doesn't have to *lead* to an increase in mental skill, it is just that they are correlated, and if a medical condition decreases both of them. they still are correlated, right? like now social interaction is less and mental skill as well. So it kind of reinforces the evidence I'd say.

[@harryduthie]

Hi Kanishk, The evidence mentioned at the end of the study definitely describes a correlation. However, the passage says there is an assumption "that people need to engage in intellectual activities... *in order to* maintain mental sharpness as they age." This implies the intellectual activities are thought to be *the cause* of people's maintained mental sharpness. The passage then goes onto say that "simply talking to other people...suffices." This means the correlation found by the study is meant to support the idea that talking to others is sufficient to maintain someone's mental skills. Answer choice (E) suggests that there is a third factor involved and that someone's social interactions and mental sharpness are both affected by their health. This reduces the force of the support provided by this correlation, making (E) the answer to this question. I hope that helps!

[@Hill958]

I think this series can be dubbed as going from 710 to 760

[@PhenomX1998HD]

I still dont understand the question 2, why exactly is B not the option? If the option says the test was more mathematical based than social conversation than this weakens the test as an evidence right?

[@PhenomX1998HD]

How can we infer from the statement that quantitively abilities to analyze come at the very end of the study? The option very clearly says that study is akin to mathematical PROBLEMS than socializing. The explanation provided feels like forcing a maybe correct option to wrong. Can someone help me out with better reasoning?

[@PhenomX1998HD]

And with Option E. It doesn’t really weaken the test because it says the sharpness decline is due to mental illness which causes further isolation. But it doesn’t really target our evidence as the evidence says more social interaction is assumed to sharpen your mental skills. In my opinion they are 2 different cases.

[@GMATNinjaTutoring]

I'm not 100% sure you're clear on what we're being asked to do on this question, but I could easily be wrong. Check out what I've written below to see if it answers your question, but please tell me if I've missed anything or misinterpreted what you've written. The claim in the passage is that social interaction is sufficient to maintain mental sharpness as a person ages. We're not told how the passage defines mental sharpness, but the passage suggests that talking to other people is enough to maintain it. The evidence provided is the study showing a correlation between a person's level of social interaction and their mental skills. Answer choice (B) tells us the tasks in the study evaluating mental sharpness were closer to mathematical tasks than to conversation. We weren't told that mental sharpness was equivalent to socializing or even that it was based on socializing in the passage. In fact, the passage didn't tell us how to define mental sharpness at all, so using mathematical tasks could be a reasonable way to measure mental sharpness. The suggestion is now that the more social interaction a person has, the better they will perform on these mathematical tasks (which are a proxy for mental sharpness). This doesn't weaken the force of evidence in the passage because we're still saying social interaction correlates to mental sharpness, so (B) is not the answer to this question. While the evidence from the study suggests social interaction correlates to mental sharpness, this is used in the passage as evidence that social interaction causes the retention of mental sharpness. Answer choice (E) suggests there's another factor at play. If a person stays healthy, they can continue their social interactions and keep their mental sharpness but if they get ill, their mental sharpness will decline and their isolation will increase. This suggests that it's not social interaction that CAUSES the retention of mental sharpness, but remaining healthy that causes the maintenance of both social interaction and mental sharpness. This undermines the force of the evidence provided, which is why (E) is the answer to this question. I hope that helps!

[@nipunhnarang2458]

Hi sir, I have a doubt in Ques 3. How can we comment on revenue going down? I was able to interpret this answer choice in 2 ways: 1) If the no. of copies are the same. Are we assuming that the balance remaining after the 4.50$ prepaid recharge was carried forward. If we say that 2$ out if the 4.50$ were used we are still left with $2.50 that technically we will be able to use later on, and as the no. of copies haven't changed, we can say that the overall cost to the avg user will be lower , hence revenue will be lesser. OR 2) Will we consider the option like this: since it is saying less than 90% is used, we will infer that 10% + was wasted by the user as he fulfilled his requirement and was in line with the librarians statement that total usage remains same . It will be great if you can actually share a concept behind how to stick to one approach in situations and avoid such confusion on the test.

[@GMATNinjaTutoring]

Hi there, I'm guessing you're referring to answer choice (D) in this question when you talk about the revenue going down, but please tell me if I've got that wrong. We can calculate the cost of the cards from the passage at $4.50 each (50 copies at 9 cents per copy). If a card is used to exactly 90% of its capacity, the person who's bought that card will have paid $4.50 to make 45 copies. This is the same amount they would have paid if they hadn't bought the card and used the old system. We're also told in the passage that the number of copies made in the library will remain essentially unchanged. This tells us that if the cards are used, on average, to less than 90% of their capacity, revenue from photocopying will increase. If the cards are used to more than 90% of their capacity, revenue from photocopying will decrease. Using the passage and (D) alone, there is no indication of whether the cards will be used to their full capacity or left with spare capacity available. They might be used, on average to 20% of their capacity, in which case revenues will increase, and they might be used on average to 95% of their capacity, in which case revenues will increase. Since we can't tell which of these outcomes will occur, we can't conclude (D) based on the information in the passage, so we can eliminate (D). As to your two interpretations, I'm not sure they're all that different. If someone used 90% of a card's capacity, they still have a balance of $0.45 available. This balance can be carried forward (the passage doesn't tell us that there's a time limit on using the balance on a card.) You could also say this balance is "wasted" if it is carried forward and not ever used. This means your two options mean the same thing unless I've misinterpreted what you've said? I hope that helps!

[@gauravlagad1360]

For Q3, how is it that C can be wrong if the question was a strength question. I still feel C is wrong

[@ashrithabs5973]

Why cant option A be the right answer for the third question? Why would anyone buy the card when they have to make less than 50 copies and burn their cash ? So isnt it implied that people would buy the card when they need to make 50 copies or more ? Just curious.

[@harryduthie]

Hi Ashritha, You're totally right that someone would be burning their cash if they bought a card and made significantly less than 50 copies. However, someone might buy a card and make less than 50 copies THAT DAY. For example, they might buy a card and make 10 copies on one day, then come back the next day and make 10 more, and so on until they've used up all the credits on their card. While it's possible that a customer would ONLY purchase a copy card on days when they need to make 50 or more copies, there's no information in the passage to support this suggestion. For that reason, we can eliminate (A) as a potential answer to this question. I hope that helps!

[@hugh9768]

Thanks for the great vid! Re Q3 - I agree that the prediction in (D) is only true if copy cards are used to their full capacity, which is an assumption that isn't supported by the text. However, prediction (E) also relies on an unsupported assumption that library patrons will purchase the copy cards at all (nowhere in the text does it say that these new machines will be used). Revenue won't increase if copy cards aren't purchased and the number of copies made in the library (all on the remaining coin-operated machines) are "essentially unchanged". It seems to me that both of these predictions are equally (un)supported by the information given. Sure, a situation where none of the patrons use the new copy machines is probably less likely than at least some patrons not using their copy cards to full capacity, but it seems crazy that a question would boil down to having to make that kind of probabilistic assessment. What do you think @GMATNinja?

[@harryduthie]

Hi Hugh, Thank you! I'm pleased you enjoyed the video! However, I disagree that (E) relies on an unsupported assumption. Answer choice (E) states: Revenues from photocopying will increase *IF* copy cards that are purchased are, on average, used to significantly less than 90 percent of their capacity. This does not say that the library's revenue will definitely increase after the refit. It says the revenue will increase IF the copy cards that are purchased are used in a particular way. You're totally right that the revenue won't increase if no one buys a copy card and continues to use the old machines to make their copies, but (E) takes that into account. I hope that helps!

[@behindmyback1152]

@@harryduthie I also think the assumption that "the number of copies made in the library will be unchanged after the refit" makes it so there is not a scenario where no one buys a copy card.

[@harryduthie]

@@behindmyback1152 The administrators believe that the number of copies made on the photocopiers "will be essentially unchanged" after the copier machines are refitted. However, it's possible that every single one of these copies in the future is made using the 'old' coin-operated system. This means there is a scenario, even if it's very unlikely, that no one buys a copy card. I hope that helps!

[@mishra.pritam]

its kinda DM question

[@faisal7828247910]

A really good tutor. Thank you so much sir.

[@jagjotsingh7378]

1/3

[@shrutiv8409]

Last question was too much lol omg

[@Conk-bepis]

0:48 - "If you take a look at the official guide, I don't know why you would do this (rhetorical question) " - what does this mean ? Is the OG bad for verbal ?

[@kotim9570]

Sodhi appi point chepu

[@manvigupta5972]

Hi! Thanks for the video, it's great. Could you please explain why, in Q2, C is incorrect? Because C tells us that there is no dependency between social contact and mental skills, and that most people are good in both. (Similar to how, E says that both are not correlated but a result of one condition.) Would really appreciate the help. Thanks!

[@GMATNinjaTutoring]

The evidence cited in the passage is a study showing a correlation between the social contact people report and the state of their mental skills. The correct answer will weaken the force of this evidence. Answer choice (C) tells us that many people are proficient at both social interactions and solving mathematical problems. There can still be a correlation between these two things, it's just a lot of people will be proficient at both. This answer choice doesn't "break" or weaken the correlation in the way answer choice (E) does. Further, (C) tells us about people's proficiency in solving mathematical problems which is not necessarily the same as their mental sharpness or mental skills. Solving mathematical problems is mentioned in the passage as one way people try to maintain their mental sharpness, but we can't say that solving mathematical problems is the same as someone's mental skills. This is an additional reason why we cannot say (C) weakens the force of evidence provided by the correlation. I hope that helps!