Q20 - Whoever murdered Jansen was undoubtedly

[ManhattanPrepLSAT1]

It’s important on this one not to get lost in the weeds. We know that the murderer could have been either Herbert or Samantha. We know this because they were both in Jansen’s office, and the murderer must have been in Jansen’s office. But this doesn’t mean that the murderer had to be either Herbert or Samantha. They’re just candidates. So by ruling out Herbert, we cannot establish that the murderer was Samantha, unless we add further information that requires either Samantha or Herbert to be the murderer.

If we knew that Samantha and Herbert were the only ones in Jansen’s office, then we would know that one of those two had to be the murderer. Then, if we could rule out Herbert, we could be sure that it was Samantha. Answer choice (C) ensures that the murderer had to be either Samantha or Herbert.

(A) doesn’t address the fundamental issue with the argument. Also, the argument didn’t leave any wiggle room for whether the footprints were left, but simply not found. The second sentence clearly states that if Herbert had committed the murder, the police would have found his footprints _ not that he merely would have left footprints.
(B) is maybe true and makes sense given the context but doesn’t ensure the conclusion follows from the evidence.
(C) guarantees that either Herbert or Samantha had to be the murderer and thus ensures the conclusion is true, if all the evidence is true.
(D) is not relevant. Just because the footprints were not Jansen’s doesn’t mean that they had to be Samantha’s.
(E) undermines the conclusion. The correct answer to a sufficient assumption question will always support the conclusion.

[linzru86]

I originally chose C because I saw that there could be more than one person in her office right away. But, I second guessed myself when I came to E. You say that E undermines the conclusion but how does it do so? I could see commonsense-wise how it would but one of the requirements of Samantha being the murderer is "she would have avoided leaving behind footprints or fingerprints" Doesn't that mean she would not have left fingerprints and therefore if she were the murderer those fingerprints that were found could not have been hers as E states? Or is this reasoning wrong because "avoid" here just means that she would have "tried not to" leave fingerprints? I just saw both C and E being necessary assumptions.

[jenndg100380]

You say that E undermines the conclusion but how does it do so? I could see commonsense-wise how it would but one of the requirements of Samantha being the murderer is "she would have avoided leaving behind footprints or fingerprints" Doesn't that mean she would not have left fingerprints and therefore if she were the murderer those fingerprints that were found could not have been hers as E states?

I could be wrong, but I think E undermines the conclusion because it says that "If Samantha was the murderer, she would have avoided leaving behind footprints OR fingerprints." (It doesn't necessarily mean she would have avoided both.) The police did end up NOT finding footprints and finding fingerprints. So, if Samantha is the killer, the fingerprints could be hers. If they weren't hers, the conclusion wouldn't necessarily follow, thereby undermining the conclusion.

Someone please chime in if I'm not explaining this correctly.

Thanks.

[ManhattanPrepLSAT1]

I just saw both C and E being necessary assumptions.

Let's start by addressing that this is a sufficient assumption question. So that changes what we're looking for in the answer choices. For a sufficient assumption question, the correct answer should prove the conclusion.

Answer choice (E) undermines the conclusion because if the fingerprints found at the scene of the crime were not Samantha's, then applying the same justification the argument uses to dismiss Herbert as the Killer we could dismiss Samantha as the killer. That would directly challenge the conclusion that Samantha must be the killer.

I love the discussion on this question! It's definitely challenging...

[apom22]

This question is tricky. The way I read it I thought that Jansen was murdered in his office But the argument does not say that.

[trulybird]

You say that E undermines the conclusion but how does it do so? I could see commonsense-wise how it would but one of the requirements of Samantha being the murderer is "she would have avoided leaving behind footprints or fingerprints" Doesn't that mean she would not have left fingerprints and therefore if she were the murderer those fingerprints that were found could not have been hers as E states?

I could be wrong, but I think E undermines the conclusion because it says that "If Samantha was the murderer, she would have avoided leaving behind footprints OR fingerprints." (It doesn't necessarily mean she would have avoided both.) The police did end up NOT finding footprints and finding fingerprints. So, if Samantha is the killer, the fingerprints could be hers. If they weren't hers, the conclusion wouldn't necessarily follow, thereby undermining the conclusion.

Someone please chime in if I'm not explaining this correctly.

Thanks.

I think "avoid leaving A or B" means she doesn't leave neither. Is that correct? This is a grammar thing...


thanks.

[timmydoeslsat]

You say that E undermines the conclusion but how does it do so? I could see commonsense-wise how it would but one of the requirements of Samantha being the murderer is "she would have avoided leaving behind footprints or fingerprints" Doesn't that mean she would not have left fingerprints and therefore if she were the murderer those fingerprints that were found could not have been hers as E states?

I could be wrong, but I think E undermines the conclusion because it says that "If Samantha was the murderer, she would have avoided leaving behind footprints OR fingerprints." (It doesn't necessarily mean she would have avoided both.) The police did end up NOT finding footprints and finding fingerprints. So, if Samantha is the killer, the fingerprints could be hers. If they weren't hers, the conclusion wouldn't necessarily follow, thereby undermining the conclusion.

Someone please chime in if I'm not explaining this correctly.

Thanks.

I think "avoid leaving A or B" means she doesn't leave neither. Is that correct? This is a grammar thing...


thanks.

If Samantha committed the murder, then she would have avoided leaving footprints or fingerprints.

It could be the case that she avoided leaving both when you read this premise in isolation. However, we must have one of those be present to have a chance of Samantha being the murderer.

The other premise said that if Herbert committed the murder, then the police would have found his fingerprints or footprints.

We know that both of those individuals were in the office on the day of the murder.

The police found fingerprints but no footprints. The fingerprints were not Herbert's.

This rules out Herbert as the murder. Via the contrapositive, we know for a fact that if his footprints and fingerprints are not there, then he did not do it.

This argument concludes that Samantha must be the killer.

For this to be true, we could plug in a variety of things to force this. The sufficient assumption in this case was that those two individuals were the only individuals in the room. This forces Samantha to be the killer since Herbert is logically ruled out.

For practice on sufficient assumptions, you could come up with hypotheticals that allow you to conclude that Samantha must be the killer.

Such as:

If Samantha is not the killer, then Herbert is the killer.

Samantha is not the killer only if Herbert is the killer.

[trulybird]

Thank you timmydoeslsat. Really appreciate your reply!

[jpchris3]

Hi,

I'm still a bit confused about the "or" language:

I was under the impression that on the LSAT, "or" is inclusive:

A or B means A or B or both

In this case,

"avoid leaving behind footprints or fingerprints" ... this only means one or the other?

Can someone clear this up?

Thanks

[porsupuesto3798]

I think the correct explanation should be like this.
The reason not to choose (E) is that (E) is necessary but not sufficient. It could be that someone else is also at the criminal scene and commits crime.

(C) on the other hand is a sufficient condition.

The question is asking a SUFFICIENT choice. (C)　is the one. If the only possible people in the office is S and Herbert and Herbert was excluded, then it must be Samantha

[wguwguwgu]

It was the butler.

[austindyoung]

It was the butler.

+1

[hakopis]

This argument concludes that Samantha must be the killer.

For this to be true, we could plug in a variety of things to force this. The sufficient assumption in this case was that those two individuals were the only individuals in the room. This forces Samantha to be the killer since Herbert is logically ruled out.

Just to clarify:
(H)erbert / (S)amantha
a = fingerprints
b = footprints

H --> a or b | ~a & ~b --> ~H

S --> ~a or ~b | a & b --> ~S

If the above is diagrammed correctly, then shouldn't Samantha be ruled out as well?

However, on the nth time reading the passage, I believe that in this case, diagramming would further complicate matters.

The stimulus says:
"Whoever killed James, was in his office"
In office ---> killed James (A --> B)

"Sam and Herbert were in his office"
A;
"Sam or Herbert killed James"
Therefore, B

Now, the conclusion is drawn by deducing that, if one of two (Sam & Herb) people were in the office, and the fingerprint's at the crime scene *did not* belong to Herb, then the only alternative is Sam.
Of course, to undermine this we could bring up that someone else could have been there. But to sufficiently prove the conclusion, Sam & Herbert would have to be the only one's in that office, thus (C) is the best answer choice.

Question:
Does "Whoever" indicate a necessary or sufficient condition?

B/c I originally had it as:

Killed James --> In office
Sam & Herb in office;
Therefore Sam or Herb killed James

But this would be affirming the antecedent, and the stem asks us to justify the conclusion.

[judaydaday]

This argument concludes that Samantha must be the killer.

For this to be true, we could plug in a variety of things to force this. The sufficient assumption in this case was that those two individuals were the only individuals in the room. This forces Samantha to be the killer since Herbert is logically ruled out.

Just to clarify:
(H)erbert / (S)amantha
a = fingerprints
b = footprints

H --> a or b | ~a & ~b --> ~H

S --> ~a or ~b | a & b --> ~S

If the above is diagrammed correctly, then shouldn't Samantha be ruled out as well?

However, on the nth time reading the passage, I believe that in this case, diagramming would further complicate matters.

The stimulus says:
"Whoever killed James, was in his office"
In office ---> killed James (A --> B)

"Sam and Herbert were in his office"
A;
"Sam or Herbert killed James"
Therefore, B

Now, the conclusion is drawn by deducing that, if one of two (Sam & Herb) people were in the office, and the fingerprint's at the crime scene *did not* belong to Herb, then the only alternative is Sam.
Of course, to undermine this we could bring up that someone else could have been there. But to sufficiently prove the conclusion, Sam & Herbert would have to be the only one's in that office, thus (C) is the best answer choice.

Question:
Does "Whoever" indicate a necessary or sufficient condition?

B/c I originally had it as:

Killed James --> In office
Sam & Herb in office;
Therefore Sam or Herb killed James

But this would be affirming the antecedent, and the stem asks us to justify the conclusion.

I would think it would be

Murderer-->in office.

This conditional still leaves out the possibility that someone other than Sam and Herbert was in the office.
Which is why (C) is a sufficient assumption - it qualifies the necessary/ rules out the possibility of the other people.

Murderer --> in office, either Sam or Herbert

Then when you rule out Sam, Herbert is the only other possible suspect.

[oyxy1111]

Is there anyone who notices there might be a key point we might have misses - what if Jansen murdered himself?

That's why I chose (D), to rule out this possibility.

Any thoughts?

[tommywallach]

You can't murder yourself. Murder refers to the killing of another.

-t

[15904273396]

I originally chose E but later noticed something wrong.
E actually leads to two different possibilities. One, S was the killer and she successfully avoided leaving behind both footprints and fingerprints. Two, S wasn't the killer and someone other than H and S was the killer.
So if E is assumed you cannot properly draw the conclusion that S was the killer. But if C is assumed that very conclusion can be properly drawn. And C has nothing wrong with the claim that if S was the killer she would have avoided leaving footprints or fingerprints behind- she successfully avoided leaving behind footprints you see?
Not a native speaker so pls pardon my language. Hope this might help clear things up.

[roflcoptersoisoi]

Stimulus: This is a stimulus replete with conditionals, however I decided to use the core method for this question.

The author concludes that Samantha is the killer because :
(1) She and Herbert were both in the office on the day of Jansen's murder.
(2) The killer must have been in the office on that day.
(3) If Herbert was the killer then the police would have found his left fingerprints or footprints at the scene of the crime.
(4) If Samantha was the killer she would not have left fingerprints or footprints at the scene of the crime.
(5) The fingerprints found at the scene were not Herbert's.

Gap/flaw: The author takes for granted that Herbert and Samantha were the only people in the office.
Perhaps there was someone else in the office that killed Jansen and they are the ones who left behind the fingerprints in question. Just because Herbert and Samantha were both in the office and Herbert was not the killer, we cannot conclude that it must have been Samantha.

(A) This is irrelevant. The fact that police would have found footprints at the scene of the crime had they been present does not guarantee that Samantha is the killer. If the police had indeed found footprints, presumably they would not have been Samantha's because we're told if Samantha did indeed kill Jansen she would not have left any. Indeed, if the police found footprints, perhaps they were left by a third suspect who is the real killer.


(B) I initially thought this was a strengthener but this in fact has no bearing on the argument. If this was added to the existing premises, we could not conclude unequivocally that Samantha killed Jansen, because the author overlooks that there may have been other people in the office on the day of the murder who could have committed the murder. If the office was the he scene of the crime, it could still be conceivably true that the fingerprints left behind were left by a a third suspect who is not Samantha.

(C) This looks good, and it matches nicely with the flaw we anticipated. We know that if Herbert killed Jansen then the police would have found his fingerprints. Since the the police did not find them it follows that he did not kill Jansen. If in addition to the existing premises, we suppose that nobody else was in the office then it follows logically that Samantha was the killer. Note, this does not necessarily mean that the fingerprints were Samantha's because we're told she wouldn't have left any if she killed Jansen. Thus the fingerprints could have been left behind by someone on the previous day who had nothing to do with the crime.

If we know that :
The killer was definitely in the office on the day of the murder
Herbert and Samantha were the only one's in the office as stated by this answer choice
Herbert is absolved of any culpability given that the fingerprints are not his, then it logically follows that Samantha is the killer.
We care about the fingerprints insofar as they can be identified as Herbert's but they weren't.

(D) At first I thought this was a necessary assumption but it's not because it fails the negation test, i.e., even if the footprints were Jansen's Samantha could have killed her because we're told that Samantha wouldn't have left any if she killed her. In fact this answer choice is irrelevant. Just because the prints were not Jansen's does not guarantee that Samantha killed her. The footprints could have been left by a third suspect who is the real killer (remember we're not explicitly told that samantha and herbert were the only ppl in the office on the day of the murder, the author is assuming this).

(E) This has no effect on the argument. I first I thought it weakened the argument, but it doesn't necessarily do that either. If the fingerprints were not Samantha's it does not make it less likely that she is the killer because we're told that she wouldn't have left any if she was the killer. The fact that the fingerprints were not Samantha's doesn't guarantee that she's the killer either nor does it doesn't preclude the possibility that the prints belong to a third person who was could have been in the office and killed Jansen.

[lee890]

Just to confirm...We an only use the conditional logic that was given about Herbert, and not the conditional logic about Samantha (that she would have avoided leaving behind footprints/fingerprints)?

I chose E because I wrote this out for Samantha's part:
Samantha is the murderer --> ~fingerprint + ~footprints
Contrapositive: Fingerprints OR footprints --> Samantha is not the murderer

Therefore Samantha can't be the murderer if the fingerprints are hers?

However, I do understand the discussion above that if we only consider the info about Herbert, than Samantha could possibly be the murderer.

[jeanne'sjean]

Answer choice (E) undermines the conclusion because if the fingerprints found at the scene of the crime were not Samantha's, then applying the same justification the argument uses to dismiss Herbert as the Killer we could dismiss Samantha as the killer. That would directly challenge the conclusion that Samantha must be the killer.

I understand why (E) undermines the conclusion. But I have a question that when you say the words in bold which I think is from the premise "Since the fingerprints were not Herbert's, he is not the murderer". But I think you have deemed it as an isolated rule. Doesn't it come from the contrapositive of the previous sentence that "if Herbert had been the murderer, the police would have found his fingerprints or footprints"? That is not the same rule applied to Samantha.

Put simply, my question is if the second last sentence can be directly applied to Samantha?

THANKS!