Q18 - Some planning committee members

[dayme11]

Hi,

I don't understand why the answer is E. It says that NO one who is on the planning committee lives in the suburbs why would the answer be (E) SOME do not live instead of (B) NO person in the committee lives in the suburbs. I don't know what I am missing here.

[bbirdwell]

As usual, the best idea is to get a good grasp of the argument before going to the choices.

1. some members ---> financial interest

2. member --> ~live suburbs

3. many members ---> work suburbs

Take a moment to see what overlaps. We cannot be sure that the "some" and the "many" have any overlap at all. (Only two "most" statements are guaranteed to overlap.) The only overlap we have is from 1 to 2 and from 2 to 3.

We can conclude that some members with financial interest do not live in the suburbs. (1+2)

We can also conclude that some members work in the suburbs but do not live there. (2+3)

Finally, we can conclude that some members neither live nor work in the suburbs.(2+3)

So the question is, which choice is provable?


As you can see, (E) is a straightforward combination of statement 1 and 2, though there is an element that is easily overlooked: the word "persons."

We know from combining statements 1 and 2 that some MEMBERS with financial interest do not live in the suburbs. This is because some members have financial interest, and members do NOT live in suburbs.

Therefore, as (E) says, some "PERSONS" with financial interest (the construction industry members) do not live in the suburbs. This is because, naturally, it is reasonable to infer that members are persons.

Now, notice the word "persons" in (B).

Do you see the error?

[nfpi2006]

I still don't get it. The text clearly identifies NO ONE on the committee, which i feel is a precedent for SOME planning members with a financial interests (construction industry). It starts with a specific group within the larger group then draws a link from a larger group.

So how about it be E and not B?

[tianfeng102]

A person is not necessarily a planning committee member.

What you have missed is the possibility that some persons who 1) are not on the planning committee; 2) have a significant financial interest in the planning committee's decisions; and 3) live in the suburbs. It has not been ruled out by the premises. Hence, answer B is possibly wrong.

I still don't get it. The text clearly identifies NO ONE on the committee, which i feel is a precedent for SOME planning members with a financial interests (construction industry). It starts with a specific group within the larger group then draws a link from a larger group.

So how about it be E and not B?

[ManhattanPrepLSAT1]

There is already a great amount of discussion on this question but I'll add my thoughts here anyway!

There are three statements that rely on logic: either conditional statements or quantified statements.

I can use notation to see the statements more clearly.

PCM some SFI
PCM ---> ~LS
PCM some WS

I can combine the first and second statement to get

SFI some ~LS

and I can combine the second and third statement to get

WS some ~LS

But I cannot draw an "all" or a "no" statement regarding people who have "significant financial interests," as is addressed in answer choice (B).

(Formal Notation Key: PCM = planning committee member, LS = lives in the suburbs, WS = works in the suburbs, SFI = significant financial interests)

Further note on reading quantified statements: "A some B" can be read as "some A's are B's."

I hope that helps!

[deweykang]

I (was) puzzled about (D). I crossed out E because of the 'Some persons', but I understand completely why the 'persons' on (E) is relevant as opposed to the 'persons' on other choices.

Generally speaking, are we dealing with the subset (PCM in construction industry) within the larger (PCM group as a whole) and the larger group itself? The first sentence provides us with the information of the subset and the second sentence gives us the information about the whole group.

In that case, I could see why we're unable to prove D - while we know that some PCM members (as a whole) work in the suburbs, we don't know if any of them are those in the construction industry.

I initially read the 2nd sentence to involve the same PCM group as those mentioned in the 1st sentence (those in the construction industry). Having understood the stimulus like that, I had trouble understanding why it was incorrect to infer that 'some of these guys do not work in the suburbs' from the fact that 'some work in the suburbs'...

[jamiejames]

There is already a great amount of discussion on this question but I'll add my thoughts here anyway!

There are three statements that rely on logic: either conditional statements or quantified statements.

I can use notation to see the statements more clearly.

PCM some SFI
PCM ---> ~LS
PCM some WS

I can combine the first and second statement to get

SFI some ~LS

and I can combine the second and third statement to get

WS some ~LS

But I cannot draw an "all" or a "no" statement regarding people who have "significant financial interests," as is addressed in answer choice (B).

(Formal Notation Key: PCM = planning committee member, LS = lives in the suburbs, WS = works in the suburbs, SFI = significant financial interests)

Further note on reading quantified statements: "A some B" can be read as "some A's are B's."

I hope that helps!

could you explain how you combined the first and second part?

[timmydoeslsat]

Here is how I diagram this one.

PCM (CI) SOME SFI

PCM ---> ~Live Sub

PCM SOME Work Sub

Those are the facts given to us. I have 2 SOME statements that have a common variable with an all statement involving the sufficient condition.

I can infer what choice E states by doing the following.

PCM (CI) SOME SFI
PCM ---> ~Live Sub

SFI SOME PCM (CI) ---> ~Live Sub

In which case I can conclude that I have SFI SOME ~Live Sub


The other inference I could make, and would have been an equally valid inference/correct answer, would be:

PCM ---> ~Live Sub
PCM SOME Work Sub

Work Sub SOME PCM ---> ~Live Sub

In which case I can conclude that I have Work Sub SOME ~Live Sub

[chess1432]

Why not C?

[ECMH05]

Why not C?

Bump. Wondering this as well.

[aznriceboi17]

Why not C?

Bump. Wondering this as well.

C is wrong because it is possible that all the planning committee (PC) members with a significant financial interest (SFI), as well as all non PC members with a SFI do not work in the suburbs. We're only given that some PC members work in the suburbs, so it's possible that all the PC members who work in the suburbs do not have a SFI. We're given no restrictions on where non PC members work, so it's also possible that all non PC members with SFI do not work in the suburb.

----

Adding on my own question:

To double check, the first sentence does not preclude there being PC members who have SFI who do NOT represent the construction industry, right?

[Awesomesauce]

Sorry - why not A? I thought that worked out as well.

[christine.defenbaugh]

Great discussion going on here, and some excellent breakdowns above, from a number of people!

I'd like to add in my own view on this question. Because this is a must be true inference question, we know that the answer is going to be 1) unpredictable and 2) fully supportable. The stimulus has a laundry list of facts we have to sort.

One thing to notice is that the entire stimulus is about the planning committee members.

Some PC have SFI.
Some PC are CI.
No PC live in suburbs.
Some PC work in suburbs.

Now, we also know, from the first sentence, that there's some crossover between the PC-SFI and PC-CI groups, but we don't know how much.

What's critical to see though is how much we don't know. We don't know anything about the whole group of SFI, or CI, or live-suburbs, or work-suburbs! Why not? Because all of our information is simply about the PC who do or do not do those things! We don't know a thing about the non-PC who do any of that.

The only answer choice that we can absolutely support is (E): some SFI do not live in the suburbs.

To figure out if this is supportable, start with the SFI. We know from the first sentence that at least one person is on the PC with an SFI. Let's call him Joe. We also know that NOBODY on the PC lives in the suburbs - and that includes Joe. So there's at least one person - Joe - who is PC, SFI, and doesn't live in the suburbs.



The Unsupportable

(A) and (B)
Both of these answers attempt to make a claim about the entire group of SFI. But we only have information about the SFI on the PC. If there are SFI who are not on the PC, we don't have a clue what they do - whether they live in the suburbs, whether they are in the construction industry, etc.

(C) and (D)
Both of these answers take 2 groups that may overlap completely, partially, or not at all and tries to pin them down.

(C) We don't know that SFI and work-suburbs overlap at all. We know at least one SFI is on the PC. And we know that at least one work-suburbs is on the PC. They don't have to be the same person though.

(D) Similarly, CI and work-suburbs might overlap completely - i.e., have exactly the same members. All we know is that some CI are on the PC, and some work-suburbs are on the PC. The two groups might be the same people.



*To address aznriceboi17's question: No, I don't think the first sentence precludes the possibility of having PC-SFI who are not CI. The first sentence simply says that some PC-CI are also SFI. It does not explicitly say that ONLY those PC-CI are PC-SFI. However, I'd be surprised to see them test that particular distinction after using that syntax. Note that we can eliminate (A) without splitting that particular hair.


Please let me know if you have any additional questions!

[legenda689]

sorry guys I still don't get it.
the way i see it is there is a big group PC and there is a subgroup FI. so if NO ONE in the group (PC) lives in suburbs how can a some people of that subgroup LS? shouldn't it be that no FI - LS?

[christine.defenbaugh]

sorry guys I still don't get it.
the way i see it is there is a big group PC and there is a subgroup FI. so if NO ONE in the group (PC) lives in suburbs how can a some people of that subgroup LS? shouldn't it be that no FI - LS?

You would be totally right if we knew for sure that ALL the FI in the entire universe were within the larger group PC. But we don't know that!

The stimulus tells us that some planning committee members have significant financial interests, but it does not tell us that everyone in the universe with a significant financial interest is actually on that planning committee!

If I told you that some of the apples at the store were red, would that mean that red things only exist at the store? Of course not! So red would be a subgroup of apples at the store, but it could also be a subgroup of *stuff outside the store*. We don't have any knowledge about that!

So, what if there were a guy named Bob who had a significant financial interest in the committee's decisions, but was NOT himself a planning committee member. That's okay - the stimulus does nothing to prevent his existence. And let's say Bob lived in the suburbs. Again, there's nothing in the stimulus to stop that from happening. So it could be possible that someone with a significant financial interest lived in the suburbs - as long as they weren't on the planning committee to begin with.

Does that help clear that up a bit?

[hakopis]

Wasn't sure about the answer at first, BUT I found a logical map once I saw it was (E).

Setup:

PC --(some)-- SFI or
A --(some)--B

SFI -------> RCI or
B -------> C

PC -------> ~LS or
A -------> ~D

PC --(many)-- WS or
A --(many)--E

Where:
PC = Planning committee members
SFI = Significant Financial Interest
RCI = Represent Construction Industry
LS = Live in Suburbs
WS = Work in Suburbs

Analysis:
Answer requires Quantitative Logic. QL requires a shared element, in this case PC.

QL doesn't allow combining 'some' with 'many' statements, consider:
A --(some)--B
A --(many)--E Therefore, Nothing

QL doesn't allow combining 'All' with 'many' statements, when 'All' statement is up first, consider:
A ------> D
A --(many) ~E Therefore, Nothing

QL DOES ALLOW combining 'SOME' with 'ALL' when 'SOME' statement is up first, consider:
A --(some)--B
A -------> ~D
Therefore
B --(some)-- ~D
*Found in answer (E): SFI --(some)--~LS

[Dtodaizzle]

I understand the logic behind (E), if the statement was reworded as

"some committee members with significant financial interests in the planning committee's decision do not live in the suburbs."

But the question explicitly states "some persons." Now these some persons could be committee members, but they could also be some persons with significant financial interests in the planning committee's decisions who are not committee members.

As a result, how could we infer that (E) must be true?

[JosephV]

I understand the logic behind (E), if the statement was reworded as

"some committee members with significant financial interests in the planning committee's decision do not live in the suburbs."

But the question explicitly states "some persons." Now these some persons could be committee members, but they could also be some persons with significant financial interests in the planning committee's decisions who are not committee members.

As a result, how could we infer that (E) must be true?

1) Persons with significant financial interests in the committee's decisions could be (i) committee members, or (ii) non-committee members. For example, imagine there were 4 construction companies in town. The CEO of one of those got elected to office in the local government. As a guy with knowledge of construction/planning he also got on the planning committee. Does he have financial interests when it comes to the planning of the construction of a new municipal recreation facility? You bet! What about the other three CEOs? Sure, they also have interest. So, of the four persons with significant financial interests in the committee's decision one is a committee member and the other three are not members.

2) Does anyone on the committee live in the suburbs? No! This means that the one guy (from our example above) who is a committee member and has significant financial interests in the committee's decision does not live in the suburbs, either.

3) The conclusion from 2) above says exactly what (E) states: some persons with significant financial interests in the planning committee's decisions (in our case that is the one CEO who is a committee member) do not live in the suburbs. Do we know where the other three CEOs live? No!

Because of 1), 2), and 3), the correct answer choice is (E).

[MatthewM35]

I have to disagree with the point regarding the inability to combine "all" statements with "many" statements when listed first. Formal logic provides no traditional direction in diagramming. Chains can be diagrammed in any direction so long as the variables within the arrows maintain their position relative to their respective arrow (i.e. A------>B cannot be reversed to B------>A but can be switched to B<-------A. This says the same thing).

When looking at the Logic Ladder and words synonymous to "some", "many" falls into this category. Some=Many, therefore, many can be substituted with some to make the proper additive and inherent inferences.

A <--many--> -E = A <--some--> -E

Combine common variables: A

D <------ A <--some--> -E, which can therefore be inferred to D <--some--> -E

QL doesn't allow combining 'All' with 'many' statements, when 'All' statement is up first, consider:
A ------> D
A --(many) ~E Therefore, Nothing

Wasn't sure about the answer at first, BUT I found a logical map once I saw it was (E).

Setup:

PC --(some)-- SFI or
A --(some)--B

SFI -------> RCI or
B -------> C

PC -------> ~LS or
A -------> ~D

PC --(many)-- WS or
A --(many)--E

Where:
PC = Planning committee members
SFI = Significant Financial Interest
RCI = Represent Construction Industry
LS = Live in Suburbs
WS = Work in Suburbs

Analysis:
Answer requires Quantitative Logic. QL requires a shared element, in this case PC.

QL doesn't allow combining 'some' with 'many' statements, consider:
A --(some)--B
A --(many)--E Therefore, Nothing

QL doesn't allow combining 'All' with 'many' statements, when 'All' statement is up first, consider:
A ------> D
A --(many) ~E Therefore, Nothing

QL DOES ALLOW combining 'SOME' with 'ALL' when 'SOME' statement is up first, consider:
A --(some)--B
A -------> ~D
Therefore
B --(some)-- ~D
*Found in answer (E): SFI --(some)--~LS

[TimothyS21]

I'm having trouble with seeing why D is wrong. Is it that in this case Many could indeed mean all therefore disproving that some do not live in the suburbs?