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In this article, we’ll look at the solution to this Official Guide (OG) question – CR03001.01 “Recent observations suggest” on Critical Reasoning:

CR03001.01 – 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 earth like worlds form a low percentage of the total number of planets?

[Refer to GMAT Official Guide for options].

• PQID: CR03001.01
• Difficulty Level: Hard
• Most Common Incorrect option choice: Choice A and Choice C
• Question Type: Weaken

## OG Video Solution – CR03001.01 – “Recent observations suggest…” | “Stars and Planets”

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## OG Solution – CR03001.01 – “Recent observations suggest” | “Stars and Planets”

Hi Student,

### Choice A-

The most popular incorrect answer choice, choice A, has left many students confused. And why not- it presents such a simple logic to weaken the conclusion. If astronomers have not yet attempted to study stars around which millions of planets orbit, then how can they say anything about the percentage of earthlike planets out of all- Marked choice A with this understanding? Let me tell you where you faltered.

Let’s say the astronomers studied 50 stars and found 200 planets around them. 180 of these planets are much bigger than earth.

Based on these observations, they suggested that earthlike planets form a low percentage of the planets orbiting stars in the galaxy other than the sun.

Choice A conveys that 10,000 stars with millions of planets around them have not yet been studied.

Does that raise any doubts on the justification given by the astronomers? The answer is no.

Firstly, from choice A we do not know that if studied, a significant percentage of these millions of planets will be earthlike. In other words, choice A does not convey that the other star systems will be significantly different in terms of planet sizes from the ones that have been studied. These star systems may also give similar results.

You can also understand it by considering that the set of stars studied may not be a proper representation of the other stars in the galaxy.

Secondly, the conclusion is specific to the stars in our galaxy. What if these star systems mentioned in choice A are outside our galaxy? Again, it will not have any impact.

Both these reasons do not allow us to question the justification given in the argument, and hence choice A is not a correct weakener.

A modified version of choice A that includes the two missing pieces of information can be a weakener. I would like you to try to come up with one such weakener.

What should you learn from choice A-

An incorrect answer choice may be based on a correct logical gap, just that it may skip some important aspects as choice A did here. Such an answer choice will usually be the most popular incorrect answer choice. Hence, always analyze every answer choice in detail and understand its impact on the conclusion.

### Choice C-

As per choice C,

If P1 is a planet orbiting a star similar to the sun and P2 is a planet orbiting a much smaller star.

Then P1 is more likely to be earthlike than P2.

Now, most likely, if you selected this choice, your logic would have been that most of the stars mentioned in the passage were much smaller than the sun, so most likely, the picture will change if stars similar to the sun are studied. Right?

If yes, you missed a few considerations-

• The passage only states that most of the planets that were detected were around much smaller stars compared to the sun. It does not state that sun-like stars were not studied. It is very much possible that a significant number of sun-like stars were studied, but just a few earthlike planets were found around them.
• Moreover, even if choice C is true, we do not know how many planets exist around the sun-like stars in our galaxy. (We do not even know the number of sun-like stars). If the number of such planets is very low, then the claim will stand correct even if more stars are studied.

Hence, choice C cannot be used to weaken our belief in the conclusion.

### The Correct Choice D-

This choice presents a weakness of the astronomers- they cannot easily detect a planet if the planet is smaller relative to the star it orbits.

Wait! What if most earthlike planets in our galaxy fall in this category, and therefore, it is difficult for the astronomers to detect them? The justification provided for the claim would no longer stand.

Hence, choice D is the correct answer choice.

Let’s evaluate the remaining answer choices too:

### Choice B-

The prediction given in choice B can at max strengthen the justification provided. Hence, choice B cannot be used to weaken the justification.

### Choice E-

Choice E conveys that the astronomers have not missed any earthlike planet around the stars studied. Just like choice B, this choice also supports the justification and hence is incorrect.

## Takeaways – CR03001.01 “Recent observations suggest” | CR OG Question – “Stars and Planets”

1. Read the passage carefully to understand the scope, for example this question was concerned with stars from our own galaxy and not all stars in general.
2. Analyze every answer choice in detail to understand its impact on the conclusion.
3. A choice based on a correct linkage may not always be correct.

If you want to solve more questions that give you complex answer choices, try these out:

Happy learning!
Kanupriya.

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