Recent observations suggest that small, earthlike worlds form a very

Question

Recent observations suggest that small, earthlike worlds form a very low percentage of the planets orbiting stars in the galaxy other than the sun. Of over two hundred planets that astronomers have detected around other stars, almost all are hundreds of times larger and heavier than the earth and orbit stars much smaller than the sun.

Which of the following, if true, would most weaken the above justification of the claim that earthlike worlds form a low percentage of the total number of planets?

Which of the following, if true, would most weaken the above justification of the claim that earthlike worlds form a low percentage of the total number of planets?

A. There are millions of planets orbiting stars around which astronomers have not attempted to detect planets.

B. The best current astronomical theories predict that almost all planets around other stars are probably hundreds of times larger than the earth.

C. A planet orbiting a star similar to the sun would be more likely to be earthlike in size than would a planet orbiting a much smaller star.

D. The smaller a planet is relative to the star it orbits, the more difficult it is for astronomers to detect.

E. The observations would have detected any small, earthlike worlds orbiting the stars around which larger planets have been detected.

CR03001.01

GMATNinja · Accepted Answer

I agree that some of these new questions are tricky! As usual, the exact language of the passage, question, and answer choices will help to eliminate the incorrect answers.

Let's first take a look at the passage:
  Conclusion: "Recent observations suggest that small, earthlike worlds form a very low percentage of the planets orbiting stars in the galaxy other than the sun." 
 Justification for this conclusion: "Of over two hundred planets that astronomers have detected around other stars, almost all are hundreds of times larger and heavier than the earth and orbit stars much smaller than the sun."

The question asks which answer choice would "would most weaken the above justification of the claim that earthlike worlds form a low percentage of the total number of planets." There are a couple of things of note in this question:
  It points us toward the  justification  for the claim. So, we are trying to weaken that particular piece of the passage, or the link between the justification and the passage's conclusion. 
 We need to find the answer that  most  weakens the justification -- this leaves open the possibility that  multiple  answer choices weaken the justification. We may need to eliminate the weaker weakeners (is your head spinning yet?), and keep the strongest weakener.

Take a look at (A):
 
To clarify the meaning of this sentence, note that the things  "around which"  astronomers have not attempted to detect planets are the "stars" mentioned earlier in the sentence. In other words, astronomers haven't attempted to detect planets around certain stars, and around these stars are millions of planets.

At a glance, this seems to weaken the force of the justification in the passage! Astronomers have only detected 200 planets, so perhaps these are not representative of the millions of other planets out there. Maybe a higher percentage of the not-yet-detected planets are earthlike, which would undermine the author's conclusion that a very low percentage of planets in the galaxy are small and earthlike.

After a bit more thought, though (A) is a pretty  weak  weakener (for the exact reason mentioned in the OE, which I'll try to explain a bit).

The author's conclusion is focused on the planets  in our galaxy , while (A) just tells us that we haven't yet detected a bunch of planets out there somewhere in space. Maybe the 200 planets that were already detected are all within our galaxy, while the millions of undetected planets are outside of our galaxy. In this case, the justification in the passage would not be weakened very much, because the data from the 200 planets would be much more relevant to the conclusion than would the new information provided by (A).

We don't know for sure whether this is true, so we just have to keep in mind that (A)  may  weaken the justification provided in the passage, or it may not.

Now take a look at (D):
 
The justification in the passage for the author's conclusion is that "almost all" of the 200 planets detected by astronomers are much  heavier  than the earth and orbit much  smaller  stars. From this, the author concludes that a very low percentage of planets in the galaxy are small/earthlike.

But wait -- what if astronomers just suck at detecting small/earthlike planets in the first place? Then the justification (that almost all of the detected planets are big) doesn't mean much. It just shows that we are good at detecting one kind of planet, and bad at detecting another. The link between the 200 detected planets and the conclusion is pretty much destroyed.

(D), if true, makes the justification provided in the passage kind of worthless. (A), in comparison, is the weaker weakener -- because we don't know whether the millions of undetected planets are in our galaxy, we don't know how much it impacts the force of the passage's justification.

For this reason, (A) is out and (D) is the right answer.

I hope that helps!

KarishmaB · Answer

Claim  : Small planets like Earth are a small percent of planets orbiting stars (other than Sun) in our galaxy.
- Of 200 planets examined, almost all are much larger than Earth and their star much smaller than Sun.

Which would weaken the justification of the claim?

A. There are millions of planets orbiting stars around which astronomers have not attempted to detect planets.

This says that there are millions of planets which have not been examined. Nevertheless, the sample of 200 examined show a particular characteristic. Nothing says that the sample is not representative. Sampling is a valid technique if sample is a good representation of the population. Also, we don't know whether the stars being talked about are from this galaxy.

B. The best current astronomical theories predict that almost all planets around other stars are probably hundreds of times larger than the earth.

This supports our claim.

C. A planet orbiting a star similar to the sun would be more likely to be earthlike in size than would a planet orbiting a much smaller star.

We don't know how many stars are Sun-like. If Sun-like stars form a very low percentage, Earth like planets will form a very low percentage too. We need to weaken the justification i.e. the observation.

D. The smaller a planet is relative to the star it orbits, the more difficult it is for astronomers to detect.

This says that our sample may not be representative of the population. If smaller planets are harder to detect, only large planets might have been detected. Hence, of the 200 planets, most were large because they were easy to find. Perhaps, smaller planets are harder to find and hence were not a part of the 200.

E. The observations would have detected any small, earthlike worlds orbiting the stars around which larger planets have been detected.

This tells us that small planets would have been easy to detect too. This helps our claim.

Answer (D)

Rachna23 · Answer

The argument implies that sample of 200 planets is representative of planets in entire galaxy and that percentage of earth-like planets in the galaxy is  very low . We need to weaken the claim.

A indicates that there are millions of other stars whose planets have not been detected. No one can sample millions of stars anyway, and this choice does not indicate why the sample taken is not representative.

B & E do not weaken the claim.

C is trap - it states that an earth-like planet is more likely to be found orbiting a sun-like star. In the absence of information about percentage of sun-like stars in the galaxy, it is not possible to comment on percentage of earth-like planets. Also, the argument says

D correctly point out that smaller planets (in relation to the size of star) are hard to detect. Thus the 200 planets detected cannot truly indicate the percentage of earth-like stars (as it is likely that only bigger planets were detected while many earth-like planets lie undetected).

gmatt1476 · Answer

Official Explanation

Argument Evaluation

This question asks you to identify a claim that would, if true, weaken the justification for the conclusion that only a small percentage of the total number of planets in our galaxy are formed by earthlike worlds.

The only justification given for this conclusion is that, of the over 200 planets that astronomers have detected around other stars, almost all are hundreds of times larger and heavier than the earth and orbit stars much smaller than the sun.

Any evidence suggesting that the planets the astronomers have detected may be unrepresentative of planets in general would weaken the justification this claim gives to the conclusion.

A. This may look like it weakens the justification. After all, if the total number of planets were significantly smaller than millions, then the sample size of over 200 planets would allow us to make the inference with more confidence. Nevertheless, particularly when accounting for the vagueness of the conclusion, the size of the sample is large enough to give us a reasonable degree of certainty. More importantly, though, note that the conclusion is restricted to planets orbiting stars in our galaxy. There is nothing in this answer choice to suggest that the planets it refers to are actually in our galaxy.

B. This choice strengthens the justification for the conclusion.

C. This choice does not weaken the justification for the conclusion. The only way it might do so is if it provided information showing that astronomers have mainly looked at planets orbiting an unrepresentative sample of stars, that is, a sample that is more heavily populated with planets orbiting stars that are smaller than most stars in the total star population. We are given no reason to believe this is the case.

D. Correct. This gives us a reason to think that the sample may be unrepresentative. Planets more earthlike in size may be less likely to be detected than the much larger stars that astronomers have detected.

E. This claim strengthens, rather than weakens, the argument. It implies that the astronomers' detection methods would not have inadvertently underrepresented the number of earthlike worlds.

The correct answer is D.

khan0210 · Answer

What is with the wording of the new edition of CR questions? I feel like the answer choices are extremely difficult to comprehend.

What does this even mean? 
A. There are millions of planets orbiting stars around which astronomers have not attempted to detect planets.

Astronomers have not tried to  detect planets  out of the  millions of planets  that orbit the many number of stars? Isn't it supposed to be trying to detect earth-like planets?

Moreover, the OG explanation for why A is incorrect includes "More importantly, though, note that the conclusion is restricted to planets orbiting stars in our galaxy. There is nothing in this answer choice to suggest that the planets it refers to are actually in our galaxy." 
Where does the passage explicitly narrow in on our galaxy, and exclude other galaxies?

RK007 · Answer

VeritasKarishma GMATNinja nightblade354 and other experts please help us out here!
Why is A wrong? Even after reading the OG explanation I'm not at all convinced. A seems fair. A vs D is hard. They're so close.
Any help would be appreciated. Thanks in advance

GMATGuruNY · Answer

In a sampling CR, information about A SAMPLE is used to draw a conclusion about A WHOLE GROUP.
To weaken the conclusion, the correct answer will typically indicate WHY the sample might not accurately reflect the whole group.

Case 1: https://gmatclub.com/forum/guidebook-writer-i-have-visited-hotels-throughout-the-country-and-hav-80358.html
Here, the OA suggests that poorly constructed hotels have likely been torn down.
Implication:
The visited hotels in the passage do not accurately reflect ALL hotels built before 1930.

Case 2: https://gmatclub.com/forum/people-who-h ... 23222.html
Here, the OA suggests that zoo employees with allergy issues are likely to switch to another occupation.
Implication:
The zoo employees in the survey do not accurately reflect ALL zoo employees with allergy issues.

Quote:

Recent observations suggest that small, earthlike worlds form a very low percentage of the planets orbiting stars in the galaxy other than the sun. Of over two hundred planets that astronomers have detected around other stars, almost all are hundreds of times larger and heavier than the earth and orbit stars much smaller than the sun.

Which of the following, if true, would most weaken the above justification of the claim that earthlike worlds form a low percentage of the total number of planets?/

D: The smaller a planet is relative to the star it orbits, the more difficult it is for astronomers to detect.
Here, earth-like planets in the galaxy are likely to be so small that they cannot be detected.
Implication:
The detected planets in the passage do not accurately reflect ALL planets in the galaxy.

Show Spoiler

D

A: There are millions of planets...which astronomers have not attempted to detect.
Here, there is no indication WHY the planets in red might differ from those detected by the astronomers.
Eliminate A.

Elite097 · Answer

ThatDudeKnows   avigutman   GMATNinja  If we knew that these millions of planets are in our galaxy, then would we say the data is unrepresentative (because of a small sample) or that we still do not know if it is representative or not ( given that nothing else is there to support why 200 is representative or not of millions of planets)? This for choice A

ThatDudeKnows · Answer

Sample size arguments can be tricky for exactly the reason that you've fallen into, but let's see if we can get a little clarity.

Imagine a bag of marbles. Millions of marbles. Some are red and some are blue, but we have no idea what percentage of each. You reach in the bag 200 times and pull out a marble each time. Three are blue. That seems to suggest that very few are blue, right? 200 out of millions is a small percentage of the overall, but it's still 200 trials, which is a lot, so the odds are really good that it is a representative sample of the millions.

Imagine a galaxy of planets. Millions of planets. Some are red and some are earthlike, but we have no idea what percentage of each. You reach in the galaxy 200 times and pull out a planet each time. Three are blue. That seems to suggest that very few are blue, right? 200 out of millions is a small percentage of the overall, but it's still 200 trials, which is a lot, so the odds are really good that it is a representative sample of the millions.

The argument's conclusion is that recent findings SUGGEST blahblahblah. Just because there are a ton of other planets to look at without any reason to expect them to be red doesn't weaken the suggestion.

If we only picked three marbles from the bag, sure, sample size matters. But quality of sample size is more a function of the number of things IN the sample than it is the number of things NOT IN the sample, and 200 is a lot for a binary distribution.

avigutman · Answer

There are several possible reasons for why a sample might not represent the general population that you're trying to sample. In this case, the correct answer plays on sampling bias (the planets in our sample is selected in a non-random manner, due to difficulties with detection). I don't recall ever seeing an official GMAT problem in which the size of the sample was the weakness of a statistical analysis. You'll probably benefit from learning about different statistical biases: https://en.wikipedia.org/wiki/Selection_bias I made a short video on one of them, which you can view here: https://youtu.be/zI51kLcEJDw

rikinmathur · Answer

The question is asking us to cast doubt on the author’s argument that small, earthlike words are unlikely given that other planets found in “our” galaxy are 100x larger.

Does this really weaken the argument? Even if they haven’t attempted, does that mean that there are small planets indeed…also this option doesn’t specify if it is talking about our galaxy or the universe in general. Maybe keep but most likely out.

This doesn’t weaken the argument, if anything, it bolsters the authors hypothesis. Out.

This doesn’t apply to the stars in question in this argument because the author specifies that the stars in question are those that are already much smaller than the sun. We are looking for presence of small planets around this sun. Out.

Interesting, what if it is difficult to detect smaller planets? It could be that these smaller, earthlike planets exist, it’s just that astronomers are currently unable to detect them. In this case, the author can’t say for sure that there are a very small % of these types of planets. Weakens the argument (note that we are looking for any new information that will weaken the claim so this option is valid)

Totally opposite of D, a big strengthener in a way! Out.

sk05 · Answer

How is D the correct answer choice? It mentions that smaller planets relative to the size of the stars are difficult to detect. Th option is not talking about all the small planets. It is talking about the size of the planets relative to the size of the stars.

Our argument says that the stars are smaller as compared to the sun. What if the size of the stars and the planets are almost the same? How is D making sense then?

MartyMurray · Answer

Here's the claim the support for which we have to weaken:

earthlike worlds form a very low percentage of the planets orbiting stars in the galaxy other than the sun

Here's the support for that claim:

Of over two hundred planets that astronomers have detected around other stars, almost all are hundreds of times larger and heavier than the earth and orbit stars much smaller than the sun.

Notice that the evidence is the characteristics of "planets that astronomers  have detected  around other stars."

Those characteristics of planets that astronomers have detected are that "almost all are hundreds of times larger and heavier than the earth and orbit stars much smaller than the sun."

So, the reasoning of the argument is basically that, since most planets detected are larger and heavier than the Earth and orbit stars smaller than the Sun, Earthlike worlds form a very low percentage of the planets orbiting stars in the galaxy.

Now, let's consider choice (D).

D. The smaller a planet is relative to the star it orbits, the more difficult it is for astronomers to detect.

At first this information may seem irrelevant to the argument, but if we consider it carefully, we can make the following connection.

Choice (D) says that planets that are small and orbit large stars are hard to detect. So, it may be that the reason most "planets that astronomers have detected" are large and orbit small stars is simply that astronomers have not succeeded in detecting planets like Earth, which are small relative to the stars they orbit.

Thus, (D) shows that the conclusion that "earthlike worlds form a very low percentage of the planets" doesn't necessarily follow from the evidence about "planets that astronomers have detected because the planets astronomers have detected may not be a representative sample of "the planets orbiting stars in the galaxy."

A planet almost the same size as a star would be a very big planet because stars are generally much larger than planets. Also, notice that the argument doesn't say that the detected planets are similar in size to stars. Rather, it says that the planets are "hundreds of times larger and heavier than the earth," meaning that they are still much smaller than stars.

In any case, (D) still works even if some planets are close in size to the stars they orbit because it could still be the case that planets that are small relative to the stars they orbit, as Earth is to the sun, would not be detected.

Contropositive · Answer

Hi  GMATGuruNY  I got this one wrong, and my takeaway from the question(option-A) is that ''don't assume sample bias ''unless stimulus gives some hint of it''.
But option (D) seems way too stinky for an AC for weaken type. (D) says:  the more difficult it is for astronomers to detect.  
For (D) too be valid, aren't we assuming tha t more difficult = astronomers won't find the planets?

(D) seems to say that more closer your exam gets more diffcult it is to study  means i won't study!

Granted that (A) is weak, but (D) too is no better!

I am not sure how valid are my concerns, and i would appreciate your views.

GMATGuruNY · Answer

In each of the CRs referenced in my earlier post, the OA suggests that the argument is flawed not because it hasn't studied all possible data but because   the sampled group inadvertently excludes members that would contradict the conclusion  .

OA:  The better the quality of original carpentry in a building, the less  likely  that building is to fall into disuse and be demolished. 
Implication:
The sampled group inadverently exclude hotels with poor carpentry, since these hotels have likely been demolished.

OA:  A zoo employee who develops a serious animal-induced allergy is very  likely  to switch to some other occupation. 
Implication:
The sampled group inadvertently excludes employees with allergy issues, since these employees have likely switched to another occupation.

OA:  The smaller a planet is relative to the star it orbits, the more  difficult  it is for astronomers to detect. 
Implication:
The sampled group inadvertently excludes small, earthlike planets, since such planets are difficult for astronomers to detect.

In the OAs. note the usage of terms such as   likely   and   difficult  .
Such terms do not imply that members have DEFINITELY been excluded from the sample but only that they have PROBABLY been excluded, leading the argument to draw an incorrect conclusion.

A:  There are millions of planets...which astronomers have not attempted to detect. 
This option does not in any way suggest that the sampled group of planets inadvertently excludes members that would contradict the conclusion.
In fact, it is entirely possible that a study of the remaining plantets would SUPPORT the conclusion that very few are small and earthlike.
Since the OA must clearly WEAKEN the conclusion, eliminate A.

Maan1997 · Answer

Hi, GMAT Ninja. What if in option (A) millions of planets which astronomers have not attempted to detect are of large size only, we don't know for sure that there will be a high percentage of earthlike planets out of those. Is this reasoning correct?

GMATNinja · Answer

Indeed, we have no idea what astronomers would observe if they were to take a closer look at the planets mentioned in choice (A). Maybe that new data would support the claim in the passage and maybe it wouldn't.

That's why (A) isn't much of a weakener. Sure, (A) points out that the sample size is relatively small, but we still have some strong evidence in that small sample size: "almost all are hundreds of times larger and heavier than the earth and orbit stars much smaller than the sun."

(A) doesn't give us any reason to suspect that this same trend wouldn't appear regardless of the sample size, so it doesn't do much to weaken the argument.

(D) is a much better choice because it gives us a clear reason why the data (i.e. the recent observations) are flawed. As a result, any conclusion or claim drawn from that data would be questionable.

I hope that helps!

AnkitNandwani1 · Answer

To weaken the justification of the claim that earthlike worlds form a low percentage of the total number of planets, we need to provide an alternative explanation for why astronomers have detected mostly larger planets. This explanation should suggest that the current detection methods are biased or limited in a way that would cause astronomers to miss smaller, earthlike planets, even if they are actually common.

Let's evaluate each option:

A. There are millions of planets orbiting stars around which astronomers have not attempted to detect planets.
- While this indicates there are many undiscovered planets, it does not directly address why the detected planets are mostly large.

B. The best current astronomical theories predict that almost all planets around other stars are probably hundreds of times larger than the earth.
- This supports the claim rather than weakens it.

C. A planet orbiting a star similar to the sun would be more likely to be earthlike in size than would a planet orbiting a much smaller star.
- This suggests that star type could influence planet size but does not directly challenge the detection methods.

D. The smaller a planet is relative to the star it orbits, the more difficult it is for astronomers to detect.
- This directly challenges the detection methods, suggesting that smaller, earthlike planets might be common but are simply harder to detect with current technology. This weakens the claim by providing a plausible reason why mostly larger planets have been observed.

E. The observations would have detected any small, earthlike worlds orbiting the stars around which larger planets have been detected.
- This option supports the current observations and strengthens the claim rather than weakens it.

Thus, the correct answer is:

D. The smaller a planet is relative to the star it orbits, the more difficult it is for astronomers to detect.

enirehtacgogogo · Answer

just because you did not see them does not mean they don't exist: D
A is a contender but weaker vs. D

Recent observations suggest that small, earthlike worlds form a very

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GMAT Critical Reasoning (CR) Questions

Recent observations suggest that small, earthlike worlds form a very

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