#20 - At Tromen University this semester, some students

[Administrator]

Please post below with any questions!

[ds72]

Hi, do you mind telling me how you get to answer E. I was just overall confused about how I need to justify the conclusion. I diagramed the premise as 205 218 BM and I understand that 205 BM . I just don't understand how E proves 205 not FLM

[Luke Haqq]

Hi ds72!

Happy to explain this one. Breaking it down, we have two premises:

At Tromen University this semester, some students taking French Literature 205 are also taking Biology 218.

P1: FL205 B218

Every student taking Biology 218 at Tromen is a biology major.

P2: B218 BM

We can make an inference that P1 and P2 can link:

FL205 B218 BM

Therefore, some of the students taking French Literature 205 are not French-literature majors.

Conclusion: FL205 FLM


Answer (E) states: "It is not possible to major in both biology and French literature." In other words,

BM FLM (this represents (1) BM FLM, and (2) FLM BM)


Answer (E) is right because it allows us to have this mega-chain:

FL205 B218 BM FLM

In other words, you can collapse that to FL205 FLM, the original conclusion of the argument.

Hope that helps!

[mjb514]

I do not understand this at all. Can you explain while not using the diagrams please.

[Francis O'Rourke]

Hi Mjb,

The first sentence tells us that some students at the university take both French Lit 205 and Biology 218. We do not know how many students this is, so it may be one student in the French class, it may be half of the students, it may be all of them.

Let's assume that there are three students in the french class who are also taking the Biology class. There may be more or fewer, but it could be helpful to imagine some specific students. We'll call them Jean, Louis, and Monique.

The second statement tells us that everyone at the university who is taking Biology 218 is a Biology major. Again, we don't know how many students there are in this class, but we do know that there are some students who take both this class and French Lit 205.

So what does this tell us about Jean, Louis, and Monique? They are in both the French Literature and the Biology class, so they must be Biology majors.

The conclusion states that there must be some students in the French Literature class who are not French-literature. Do we know this about our three hypothetical students? We definitely know that Jean, Louis, and Monique are Biology majors, but they might be double majors!

We now need an answer choice that says it is impossible for these three to major in both Biology and French-literature. Answer choice (E) provides exactly this.

Let me know if this helps!

[eronquillo12]

Hi- i read the explanation for why E is correct, but I still don't understand why B is wrong. Can you explain? I am having a hrd time ruling B out.

[James Finch]

Hi eronquillo,

The issue with answer choice (B) is that it doesn't rule out majoring in French literature, because a student could conceivably double major, even in unrelated academic disciplines like biology and French literature. (E) explicitly rules out this possibility and thus logically proves the stimulus's conclusion.

Now if (B) had been worded to say that "only biology majors with no other major are allowed to take Biology 218" it would have been correct, as it would have eliminated the possibility of a double major.

Hope this helps!

[ShannonOh22]

Hello! I see why E is correct, and that was my initial choice, until I second-guessed myself and went with B. I thought B might be a safer bet because it is not as restrictive as E, but this is a sufficient assumption question, so we are looking to help prove the conclusion, correct? Also - and this may just be wishful thinking - but do you have any tips or tricks to diagramming a question like this quickly? I feel like taking the time to draw out each step as one of the Powerscore Admin did in their explanation would be way too time-consuming on an actual LSAT.

Thanks!

[KelseyWoods]

Hi Shannon!

Yes, this is a Justify question so we are trying to prove the conclusion 100%. It's always important to pay careful attention to what type of question you're dealing with because that changes what types of answer choices you're looking for.

This question involves a formal logic chain. There's not really a shortcut to diagramming it--you would need to diagram each premise and the conclusion, as Luke did. He wrote out each premise separately so that you could see them but on test day, you would just go ahead and connect the 2nd premise to the first one so it's not actually that much diagramming:

Premise chain: FL205 B218 BM
Conclusion: FL205 FLM

Remember to prephrase! We're trying to prove the conclusion that some FL205 students are not FL majors based on the premise that some of them are bio majors. If we know that some FL205 students are bio majors, what else do we need to know to prove that some of them are not FL majors? We need to know that they can't major in BOTH bio and FL, which is exactly what answer choice (E) gives us. If we add that fact to the premise that some of our FL205 students are bio majors, that proves that some of our FL205 students are not FL majors.

Answer choice (B) is just a reiteration of the 2nd sentence. Only bio majors are allowed to take B218 is the same thing as saying that every student taking B218 is a bio major and you would diagram those 2 statements in identical ways. So answer choice (B) adds nothing to the argument and does not definitively prove the conclusion.

Also, back to your diagramming question: you will get faster at diagramming with practice and don't assume that diagramming necessarily slows you down. A quick and efficient diagram can actually save you time because instead of having to juggle complex relationships in your head, you have them written on the page where you can quickly refer to them. They can also help you prephrase and allow you to go through the answer choices more quickly because you know exactly what you're looking for. You don't need to diagram every conditional or formal logic relationship you encounter on the exam (and you won't have time to!) but using diagramming for particularly complex relationships or chains can save time and make you more accurate.

Hope this helps!

Best,
Kelsey