Astronomer: Most stars are born in groups of thousands, each

Let's take a look at the passage again before looking at (E).

The conclusion of the passage is: if two stars have the same composition, they must have come from the same gas cloud.

The evidence for this is:

1) Stars are born in groups and each group originates from a single gas cloud
2) Each gas cloud has a unique, homogenous composition

We're asked to find the answer choice that best strengthens this argument. (E) tells us:

There's a small gap in the passage's logic: we're not told that the chemical composition of the gas cloud is inherited by the stars it produces. So, even if there is a nice, homogeneous mix of chemicals in the cloud, maybe they get separated or skewed or changed or whatever else when the stars are created.

(E) tells us that astronomers can at least sometimes tell whether a star has the same chemical composition as its parent gas cloud. This doesn't fill in the gap in the passage's logic. The astronomer's ABILITY to determine whether a star has the same chemical composition as its parent gas cloud doesn't tell us whether the star HAS the same chemical composition as its parent gas cloud.

From the information given in (E), we don't know if the results of the test these astronomers perform would support or undermine the claim in the passage. This means (E) cannot strengthen the argument -- (E) is not our answer.

Compare this to (C):

This fills in the gap in the passage's logic perfectly. It tells us that whenever a star is formed, it has the same chemical composition as its parent cloud of gas. Since we know each cloud of gas has a unique, homogenous chemical composition, we can tell which cloud of gas a star has originated from by its chemical composition.

(C) strengthens the argument by filling in the gap in the passage's logic -- (C) is the answer to this question.

I hope that helps!

The passage already assures us that "each cloud has a unique homogeneous chemical composition". If each cloud's chemical composition is indeed UNIQUE, then we don't need to worry about clouds with the same composition.

(B) actually contradicts the argument. If (B) is true, then we CAN have clouds of gas of identical chemical composition in various parts of the universe. In that case, we could easily have two stars with the same chemical composition, even though the stars originated from two totally separate clouds (both of which had the same composition).

The astronomer concludes that two stars with the same chemical composition must have originated from the same cloud of gas -- meaning literally a single cloud, which by definition must exist in a single place.


Choice (B) states that two clouds existing in two places can have identical chemical composition.

If this statement is true, then we can picture two clouds (let's call them cloud F and cloud G), with chemical composition X. It's now possible that two stars with chemical composition X did not come from a single cloud. One star may have originated from cloud F, while another has originated from cloud G. This contradicts the conclusion that both stars must have originated from the same cloud.


(B) introduces precisely the information that contradicts this reasoning. If (B) is true, then it is possible for two stars with identical chemical composition to have come from two totally separate clouds. The cloud's composition is still unique, but it is now present in more than a single cloud.

I hope this clarification is helpful!

Hi, I chose B rather than C. Here is my thought process:
I thought Strengthen must not be an Assumption.
Here the author already assumes that stars have same chemical pattern as their parent cloud. So I felt this to be the assumption.
So something other than assumption that helps strengthen the conclusion is what I chose.

(B) Clouds of gas of similar or identical chemical composition may be remote from each other.
If identical clouds are adjacent, assuming stars form with same imprint, analysing two stars will not lead to conclusion that these are formed from same cloud. So I chose this.

(C) Whenever a star forms, it inherits the chemical composition of its parent cloud of gas.
This is already the assumption on which the author relies. So I did not choose this.

Please correct my thought process.

For option A, B, D and E---- We can say that "COULD BE". But we can't say that definitely as passage has no specific information for all of these options.


For this----- Therefore whenever two stars have the same chemical composition as each other, they must have originated from the same cloud of gas. to be true C has to be true.

2. Astronomer: Most stars are born in groups of thousands, each star in a group forming from the same parent cloud of gas. Each cloud has a unique homogeneous chemical composition. Therefore whenever two stars have the same chemical composition as each other, they must have originated from the same cloud of gas.

Which of the following, if true, would most strengthen the astronomer's argument?

(A) In some groups of stars, not every star originated from the same parent cloud of gas.
(B) Clouds of gas of similar or identical chemical composition may be remote from each other.
(C) Whenever a star forms, it inherits the chemical composition of its parent cloud of gas.
(D) Many stars in vastly different parts of the universe are quite similar in their chemical compositions.
(E) Astronomers can at least sometimes precisely determine whether a star has the same chemical composition as its parent cloud of gas.

Conclusion- whenever two stars have the same chemical composition as each other, they must have originated from the same cloud of gas.
Pre think step-In strengthen we can create a situation or a context in which the conclusion comes true or it increase the probability of success of the conclusion.With these in mind lets look at the answer choices

A-This is the opposite of what the argument states hence out of scope
B-Does not support the conclusion in any way
C-This is correct since it increases the chances that the conclusion will come true.As the star forms from its parent cloud gas it inherits(new info) the chemical composition of its parent cloud of gas hence it increases the possibility of success that they have must have originated from the same cloud of gas
D-Does not support the conclusion as it talks about stars in different parts of the universe.Stars of the universe is not the issue here
E-At least sometimes precisely determine" talks about determination of chemical composition which is out of scope.

Explanation

Question Type: Strengthen
Boil It Down (Simplified & Abbreviated Summary of the Prompt): Each gas cloud unique -> If stars have same composition, came from same cloud
Missing Information: The stars take on the same fingerprint of the parent cloud
Goal: Based on the prompt, find the option that reinforces the missing information.

Analysis: This prompt seems fair enough. Each gas cloud has a UNIQUE, one of a kind signature, so it follows that any two stars must have come from the same parent cloud, but WAIT! Just because stars may have come from the same parent cloud, does that necessarily mean that the stars would reflect that truth? Not necessarily. That is the HUGE missing gap in the logic of this argument. No question, the right option needs to fill that void that the stars reflect the chemical makeup of the parent gas cloud.

A) Irrelevant. This argument isn't claiming that all stars that happen to be in a given group originated from the same cloud. Instead, the prompt is going the other direction. It's saying that if any two stars did come from the same parent gas cloud that they would have the same chemical signature. DUMP A!

B) Out of Focus. This option just presents a random fact that totally separate from the logic of the argument. The argument doesn't need support that similar clouds can be remote. Gone.

C) Yes! This was the exact missing link that we needed. The one piece of information that this argument lacks is that the stars take on an identifiable chemical signature from the parent cloud. C gives us exactly that. With C, we far more safely say that since the parent cloud has a UNIQUE chemical composition, AND with C, stars take take on that same chemical composition, that if two stars have the same composition as each-other, then they originated from the same cloud.

D) Violently Out of Focus. This option is talking about stars "quite similar in their chemical composition". The argument doesn't deal with stars that have a similar make up. The argument deals with stars that have THE SAME chemical make up.

E) Out of Focus. This option feels more like a correct option from an Inference question. As it relates to this strengthen question, however, the prompt actually makes it clear from the phrase "whenever" stars have the same chemical composition" that the ability to ascertain the composition is present. The argument doesn't need proof for something already established. Gone.[/quote]

Hey Max,

What if option E says, Astronomers can every time find the composition of stars accurately. Will it be a correct answer. I think the problem with option E is can atleast sometimes. Please correct me if I am wrong.

Hi Alok322,

I'd be happy to help. I like the idea of using hypotheticals with options to understand the logic backing up the argument, and the question.

So, let's run with your hypothetical:
Astronomers always have the ability to precisely determine whether a star has the same chemical composition as its parent cloud of gas.

That strengthens the notion that scientists can determine composition at will; HOWEVER, there's still a colossal shift in focus between the composition of the parent cloud vs the composition of the star. What if even though every CLOUD has a unique composition, the STARS that form from different clouds have standard compositions despite which cloud they formed from? The fact that this hypothetical still leaves such a glaring hole open leaves it remaining problematic.

Compare that to option C, which provides that missing link between composition of star and parent cloud (thus resolving that horrifically problematic gap within the argument).

C is already stated in the passage. How can it be chosen again to strengthen the argument?

[quote="LithiumIon"]2016 GMAT Official Guide, Question 2, Page 502

2. Astronomer: Most stars are born in groups of thousands, each star in a group forming from the same parent cloud of gas. Each cloud has a unique homogeneous chemical composition. Therefore whenever two stars have the same chemical composition as each other, they must have originated from the same cloud of gas.

Premise: Each Star is formed from the same parent cloud of gas.
And each cloud of gas has a unique homogeneous chemical composition.


Conclusion: Whenever two stars have the same chemical composition as each other, they must have originated from the same cloud of gas.

Pre-thinking: Clouds have unique composition --> Stars are formed from this cloud --> So, each star must inherit the properties of the cloud, else they would not have the same composition as the cloud from which it originated. --> If they inherit the same property then that would mean, any two stars from the same gas, would have the same competition.

Which of the following, if true, would most strengthen the astronomer's argument?

(A) In some groups of stars, not every star originated from the same parent cloud of gas.[If they don't originate from the same parent cloud of gas, then they would not have the same composition - this kind of acts as a weakener.]

(B) Clouds of gas of similar or identical chemical composition may be remote from each other.[The question is whether the stars have originated from the same cloud of gas or not -we are not concerned about the distance between these clouds of gas - eliminate this option. ]

(C) Whenever a star forms, it inherits the chemical composition of its parent cloud of gas. [This matches with our pre-thinking and this actually strengthens the argument,
by directly telling us that the stars inherit the property.If they inherit, then two stars with the same composition must come from the same cloud of gas.]

(D) Many stars in vastly different parts of the universe are quite similar in their chemical compositions. [This does not help us in proving that two stars have come from the same cloud of gas - Eliminated.]

(E) Astronomers can at least sometimes precisely determine whether a star has the same chemical composition as its parent cloud of gas.[This is out of scope - we are not here to discuss whether Astronomers can determine something or not.]

Correct Answer C.

Conclusion: Therefore whenever two stars...cloud of gas
Premise: Most stars are born...homogeneous chemical composition
Here, my assumption to strengthen this argument was "clouds with the same chemical composition either cannot exist or do not lie close to each other".
If we negate this assumption, we can see that the conclusion gets shattered. On this basis, I chose B. Please explain where am I going wrong in my thought process.

Assumption: Parent ( Cloud ) and Child ( Star ) will have same chemical composition.
Aim: Strengthen the assumption.

(A) In some groups of stars, not every star originated from the same parent cloud of gas. - "each star in a group forming from the same parent cloud of gas", the option is stating the prompt in the wrong way.
(B) Clouds of gas of similar or identical chemical composition may be remote from each other. - Out of focus
(C) Whenever a star forms, it inherits the chemical composition of its parent cloud of gas. - Yes, if it is true, it strengthens and if not, it breaks the conclusion.
(D) Many stars in vastly different parts of the universe are quite similar in their chemical compositions. - Out of focus
(E) Astronomers can at least sometimes precisely determine whether a star has the same chemical composition as its parent cloud of gas. - It kind of strengthens but at least makes it not as strong as C. So, we can eliminate this.

Dear GMATNinja,
I've not gotten your opinion that B actually contradicts the argument.
I thought B states the location of two identical chemical composition may be far away from each other, i haven't gotten the correlation between location and composition. can you explain further why B contradicts the argument?

additional, the arguments states that each cloud has unique composition, so, if two stars are indentical, they are unlikely to from two totally separate clouds. Is my reasoning valid?

Thanks in advance

Have a nice day
>_~

Summary of question: Most stars are born in groups. Each star in the group is formed from the same cloud of gas. Each cloud has unique composition. So, we can conclude that two stars with same composition must have originated from the same cloud of gas.

Asked: To find a strengthener

Pre-think: Correct option must bring in new information that will increase belief in conclusion. We need to think of assumptions the author made to draw the conclusion and strengthen those assumptions. In the argument, we are given that each star in the same group is formed from the same cloud of gas and each cloud has a unique composition. Clearly, in order for the conclusion to be true, the stars must be inheriting the unique composition from their parent clouds. This is our assumption. A strengthener would be to agree with the above mentioned assumption.

Option analysis:
A) This option is out of scope. We are not concerned about stars in groups, but rather have a drawn a conclusion about stars which have the same chemical composition
B) Again, the conclusion doesn't talk about distance between the stars in question. Hence, this option doesn't strengthen
C) Correct. This is completely in line with our pre-thinking
D) This option doesn't provide whether these stars are in fact formed from the same cloud. Additionally, similar is different from same. So, can't compare.
E) Out of scope

GMATNinja

Does option E mildly strengthen the conclusion? Kindly help me understand on what basis would you reject option E?

(E) Astronomers can at least sometimes precisely determine whether a star has the same chemical composition as its parent cloud of gas.

It is A , the others weaken the stimuli apart from B which is irrelevant .

Explanation for C-If each star's composition is identical to that of its parent cloud, and each cloud's composition is unique, then any two stars identical in composition must have formed from the same parent cloud.

Hey Student,

Allow us to assist guide you in the right path.

You are absolutely right when you say that a strengthened need not bring a must be true condition like assumptions. However, option B does not really help you believe in the argument.

Think of like a discussion between 2 friends - Let's say you and your hypothetical friend Alex have this discussion where Alex is the author. Now, a third hypothetical guy doubts Alex's conclusion. In order to support Alex's argument, in other words, increase the third person's belief in the conclusion - what would you say given that you can choose between B and C.


I am certain you will be able to figure it out and the cloud of confusion will be removed.

Thanks & Regards