#20 - Whoever murdered Jansen was undoubtedly in Jansen’s

[Administrator]

Complete Question Explanation

Justify the Conclusion. The correct answer choice is (C)

This stimulus provides something of a murder mystery. Jansen’s murderer was in the victim’s office
on the day of the crime, and Samantha and Herbert were both in Jansen’s office on that day. Had
Herbert committed the crime, the police would have found his fingerprints or footprints at the scene.
Had Samantha committed the crime, she would have avoided leaving behind any fingerprints or
footprints. Fingerprints were found at the scene, but there were no footprints. The fingerprints did not
belong to Herbert, so it makes sense to conclude that he is not the murderer. Once Herbert has been
ruled out as a suspect, however, the writer jumps to the conclusion that Samantha must have been the
culprit. This argument has many premises, breaking down as follows:

• Premise: Jansen’s murderer was in Jansen’s office the day of the crime.
  
  Premise: Samantha and Herbert were both in Jansen’s office that day.
  
  Premise: If Herbert were the culprit, he would have left prints.
  
  Premise: If Samantha were the culprit, she’d have avoided leaving prints.
  
  Premise: The police found fingerprints, but no footprints.
  
  Premise: The fingerprints were not Herbert’s.
  
  Subsidiary
  Conclusion: Therefore, Herbert is not the murderer.
  
  Conclusion: Therefore, Samantha must be the killer.

This conclusion is not fully justified based on the information provided. It is possible that Samantha
is the killer, because we only know that she would have avoided leaving prints, so the prints found
at the scene could have belonged to her. However, this argument is not air-tight, because only two
possible suspects have been identified. Could there have been another culprit entirely? There simply
is not enough information to justifiably conclude that Samantha was the only conceivable murderer.

The question stem asks which of the answer choices allows the conclusion in the stimulus to be
properly drawn. The correct answer choice will allow the reader to justifiably rule out all other
possible suspects.

Answer choice (A): Since Herbert has already been ruled out, this answer choice merely lends
support to the assertion that Herbert could not have been the culprit.

Answer choice (B): We were told in the stimulus that the murderer was in Jansen’s office on the
day the crime took place, so this answer choice provides no additional relevant information to help
justify the conclusion that it must have been Samantha.

Answer choice (C): This is the correct answer choice. If all other possible culprits have been
eliminated (since the murderer was in the office that day, and Herbert and Samantha were the only
ones in the office on the day of the crime), then we can justifiably conclude that the only remaining
possible offender would have been Samantha.

Answer choice (D): The stimulus describes the death as a murder, so we already know that the
culprit must have been someone other than Jansen. This answer choice, therefore, offers no relevant
information to justify the conclusion about Samantha.

Answer choice (E): If the fingerprints found at the scene did not belong to Samantha, this obviously
weakens the conclusion that she was the culprit, so this answer choice does not provide an
assumption on which the argument depends.

[ehilliard]

Hi,

I started attacking this question by diagramming the conditionality. Here are my diagrams:

1) If Herbert --> fingerprints or footprints
2) If Samantha --> no fingerprints and no footprints

Since the fingerprints found were not Herbert's, I prephrased that the necessary assumption in order for Samantha to be the killer was that the fingerprints found were not hers. This led me to answer E. If Samantha was the killer, she didn't leave her fingerprints and she didn't leave her footprints. If you logically negate E, it weakens the conclusion that Samantha is the killer.

If C is true, that no one else was in Jansen's office that day except Herbert or Samantha... then the fingerprints found would have to be Samantha's or Jansen's. It therefore seemed logical to me that it would be necessary to prove that the fingerprints weren't Samantha's so Samantha could be deemed the killer.

Can you clarify this for me?

Greatly appreciated,
Erin

[Nikki Siclunov]

Erin,

Thanks for the question. Your confusion stems from your misunderstanding of the question stem: this is a Justify, not an Assumption, question. The correct answer choice, if true, must be sufficient to prove the conclusion. So, we aren't looking for necessary assumptions, which (E) would clearly be an instance of. Let's take a closer look at (C): if no one but H or S was at the scene of the crime, this would prove that either H or S was the killer. We know H cannot be, because the fingerprints were not his. So, if answer choice (C) were true, we would automatically know that Samantha was the killer. (We can also conclude that the fingerprints weren't hers, but that's an implication of the conclusion, not something that - if true - would prove it.... careful not to make a Mistaken Reversal of the third sentence).

Hope this helps! Let me know.

[ehilliard]

Ah, I absolutely see that now! Thanks for the clarification!

[Sherry001]

Hello ,
Could you please help me with my reasoning through this easy one ? I feel I'm knit picking a tad but I kind of have a problem with c.

1- Herbert committed the murder -> finger prints or foot prints
2- Samantha committed the murder -> she would not have left behind foot or finger prints.
3- the found finger prints were not Herbers
C: Samantha must be the killer

I see that this a justify question which means it has to be 100 percent airtight . But then according to our premise 2 - if the police found finger prints then by contra positive Samantha would not have committed the crime ( especially since no foot prints were found).

A) doesn't help us conclude anything about Samantha .
B) we know this . Doesn't help .
C) this 100 percent make Samantha guilty. ( but i feel it goes against the conditional logic )
D) even if they were Jansens .. He couldn't have murdered himself . So doesn't help us really say anything about Samantha .
E)weakens .

Thanks so much
Sherry

[Steve Stein]

Hi Sherry,

That's a great question—and a potentially tricky one. The author provides a few conditional statements, and it can be helpful to diagram those along with their contrapositives as we go. Whoever committed the murder was in Jenson's office on that day.

• murderer In Jensen' office
  
  in Jensen's office murderer
  (If someone was not in Jensen's office that day, they could not have been the murderer)

As you noted, both Samantha and Herbert were in the office on that day, so the contrapositive above does not apply to them (they were in Jensen's office, so they are still potential suspects).

The author goes on to say that if Herbert had been the culprit, the police would have found his fingerprints or footprints:

• • Herbert murdered Jensen police find Herbert's fingerprints or footprints
    
    police find Herbert's fingerprints or footprints Herbert murdered Jensen

Since we are soon told that the police found no footprints, and someone else's fingerprints, according to the contrapositive diagram directly above, we can rule out Herbert as a suspect—the police didn't find Herbert's prints, so he could not have murdered Jensen.

What about Samantha? The author says that she would avoid leaving fingerprints or footprints, so it seems that the fingerprints the police found must have belonged to someone else (they did not belong to Herbert either, though, as we have already established). Keep in mind that even though the fingerprints must have belonged to someone else, that does not rule out Samantha as a suspect (there is no proof, after all, that the fingerprints which were found belonged to the murderer).

So, it seems the fingerprint evidence will not help us to solve this case. How, then, can we conclude that Samantha must have been the killer? Since this is a Justify the Conclusion question, the correct answer, when added to the premises in the stimulus, will allow us to properly conclude that Samantha was indeed the culprit. Correct answer choice (C) accomplishes this: The first contrapositive diagrammed in the discussion above (in Jensen's office murderer) provides that if someone was not in Jensen's office on the day of the murder, they could not have committed the crime. If, as correct answer choice (C) provides, Herbert and Samantha were the only ones in Jensen's office on that day, then they are the only two possible culprits. And, since we were already able to establish that Herbert was not the murderer, this answer choice would bring us to the conclusion that Samantha must have been the culprit.

I hope that's helpful! Please let me know whether this is clear—thanks!

~Steve

[LSATer]

It seems to me (please correct me if I am wrong), that to really justify the conclusion you have to ignore the conditional about Samantha and just assume that she is the killer and find an answer choice that proves this 100%--which is C. Focusing on whether she is the killer or not is not what we are being asked to do. Rather, we have to accept this and prove it.

Because even after reading the explanations, I still don't understand how to consider the Samantha conditional and not have a contradiction. By the conditional, Samantha is murder---> No footprints or No fingerprints present, if fingerprints and footprints present--->Samantha is not the murder. And since they found fingerprints that would automatically rule Samantha out. I understand that the fingerprint could possibly belong to someone else--BUT the conditional doesn't say that the fingerprint present would have to belong to Samantha for her to not to be the murder. The conditional is just about the presence and lack of presence of fingerprints or footprints.

I just realized something while I was typing. Is it because the contrapositive is really Fingerprint AND Footprint present----> Samantha is not the murder? And because only one and not both were found, it allows for Samantha to still be the killer?

Thanks,

LSATer

[Kristina Moen]

Hi LSATer,

The tricky (or great!) thing about this question is that you can actually IGNORE the conditional statement about Samantha ("But if Samantha was the murderer, she would have avoided leaving behind footprints or fingerprints."). It's really just there to throw you off and is not needed for answering this question. The key to answering this question in the first sentence.

"Whoever murdered Jansen was undoubtedly in Jansen’s office on the day of the murder" can be diagrammed as:
Murdered Jansen In Office

"Samantha and Herbert were in Jansen’s office on that day." This meets the necessary condition. This should raise a red flag to you already. Being in Jansen's office is necessary for committing the murder, but it is not sufficient. Just because someone was in Jansen's office does not meet they committed the murder! And the test makers love to play with this error of reasoning, which is what they did here. Once we know Herbert did not commit the murder, the conclusion is that it was Samantha! But being in the office is not sufficient to commit the murder. There could have 100 students in the office that day! It seems like you understand why answer choice (C) justifies the conclusion here.

So let's talk about the conditional statement about Samantha (although again, it's not necessary for this question):
"But if Samantha was the murderer, she would have avoided leaving behind footprints or fingerprints" can be diagrammed as Samantha is murderer No Samantha fingerprints AND no Samantha footprints (careful there with the "or"... she doesn't leave either of them). So if we DO have Samantha fingerprints or we DO have Samantha footprints, Samantha is not the murderer (because she's too sneaky!). However, the fact that the police found fingerprints doesn't mean Samantha did not commit the murder. The fingerprints could have belonged to another student who was in the office that day.

But I do want to make sure this conditional is clarified:
If A happens, then neither B nor C happens is diagrammed as A No B and No C.

[LSATer]

Thank you, Kristina! Your explanation is very helpful. .

I knew that neither nor translates to not A AND not B, but I didn't catch that here. I didn't realize that "if Samantha was the murderer, she would have avoided leaving behind footprints or fingerprints," is essentially say no fingerprints AND no footprint. Thank you for clarifying this. Very useful.

Thanks a bunch!

LSATer

[AM4747]

Hello,

I got this right and I know why C is correct. but I have a minor question.

In the stimulus it says: If Samantha was the murderer, she would have avoided leaving finger/foot prints.

As has been explained, the above sentence does not rule out the possibility that the prints found at the murder scene belongs to Samantha. Is this because of the word "avoided"? In other words, is the reasoning that she would have avoided but not necessarily successful in doing so? If this is the case, then does the stimulus in effect mean she would have TRIED to avoid it? In general, how am I supposed to interpret such sentences? Is there an LSAT world formula?

The contrapositive is that if Samantha would not have avoided leaving prints, then she is not the murderer. Now let us try to negate answer E and see if it hurts the argument. The fingerprints found at the scene ARE Samantha's. But given that this answer is incorrect, in retrospect, it seems that the fact that Samantha's fingerprints are found at the murder scene does NOT entail that Samantha did not avoid leaving fingerprints. This sounds a bit counterintuitive to me.

Any clarification would be deeply appreciated.

All best