#20 - If the majority of the residents of the apartment

[Administrator]

Complete Question Explanation

Parallel Flaw-SN. The correct answer choice is (D)

The stimulus of this problem contains a flawed reasoning in the form of a mistaken negation. It states that:

• Most Residents Complain Exterminator

Thus,

• Most Residents Complain Exterminator

It is not a correct reasoning because even if most residents of the apartment complex do not complain, there might be other reasons for the management to engage the services of an exterminator.

Answer choice (A): This is an incorrect answer because it is a correct restatement, and thus does not parallel the mistaken negation of the stimulus. The diagram of this answer is as follows:

• Funds Sufficient Theatre Constructed

Thus,

• Funds Sufficient Theatre Constructed

Answer choice (B): This is also an incorrect answer since it is also a correct restatement (be careful when diagramming the "unless"). The diagram for this answer choice is:

• Higher Airfares Flights Reduced

Thus,

• Higher Airfares Flights Reduced

Thus it is also an incorrect answer since we are looking for a mistaken negation.

Answer choice (C): Even though this choice contains flawed reasoning, the flaw is not a mistaken negation. The diagram for this answer choice is:

• Mayor Approve
  Start Building Project AND
  Town Council Approve

Thus,

• Mayor Approve Start Building Project

As we can see, it is an incomplete mistaken reversal. Either way, it is not the mistaken negation that we are looking for.

Answer choice (D): This is the correct answer choice. The diagram is as follows:

• Certain Band Play Most Employees Attend

Thus,

• Certain Band Play Most Employees Attend

Since this is a mistaken negation just as the stimulus, it is therefore the correct answer.

Answer choice (E): Although this answer choice contains flawed reasoning, it does not contain a mistaken negation. The diagram for this answer choice is:

• Principal Approve
  Dress Code Change OR
  2/3 Parent Council Approve
  
  Principal Approve Dress Code Change

This is not a correct contrapositive. The contrapositive of the premise should be:

• Principal Approve
  AND Dress Code Change
  2/3 Parent Council Approve

This flaw, however, is different from a mistaken negation, so this is not a correct answer.

[kashb]

I have a question about the unless diagram for answer choice B. I thought to negate 'unless' that you use the statement modified by unless as the necessary statement and the other statement is negated and used as the sufficient statement.

I am not understanding how this applies to the diagram for answer choice B below. Please help clarify. In a way I can see how the diagram comes, but in my head I got to that by rephrasing the answer to if the airlines doesn't collect higher airfares, then the number of flights wont be reduced.

**I think I just figured out that I was using the wrong terms that were modifying 'unless'. The phrase that is necessary, will that typically come after the word unless?**

[EL16]

Hi,

I have the same question as posted by the user above me (Kashb). I got this question correct, but am just looking through all the answer choices to make sure I properly diagrammed each. In the post above (by Administrator), it makes a point for answer choice B to ensure you diagram the "unless" correctly. Yet, it seems that the diagram pictured may be incorrect or I am incorrect?

For answer choice B, I had:

Premise: # of flights operated reduced airlines can collect higher airfares
Conclusion: airlines CANNOT collect higher airfares # of flights operated NOT reduced

Can you confirm which way is correct (this or the one diagrammed by the administrator post above)? I want to ensure I am understanding the "unless" technique properly.

Thanks,
Elana

[Jonathan Evans]

Hi, KashB and Elana,

Good questions.

Elana the way you have it diagrammed AND the way the administrator diagrammed it are both correct.

"Unless" introduces a necessary condition and can be interpreted in the manner in which KashB described it:

• (1) Put the idea introduced by "unless" on the necessary side of the conditional; negate the other idea and make this negation the sufficient condition.

Alternatively, (2) you can interpret "unless" (and "without," "except," "until") as "if not." In this case, you negate the idea that follows "unless" and make it the sufficient condition; you leave the other idea not-negated and use it as the necessary condition.

For example:

• I'm going to be totally bummed unless I'm first in line for the new Star Wars movie.
• (1) NOT totally bummed first in line for the new Star Wars movie
• (2) NOT first in line for the new Star Wars movie totally bummed

What do you notice about approaches (1) and (2) above? They are contrapositives of each other! In other words, both ways of dealing with "unless" work because either you get the conditional in one form or you get the same conditional in its contrapositive form. Either approach conveys the same logical relationship.

In fact, it would be prudent to review the process of creating contrapositives as this is an essential skill for success on the LSAT. When students encounter a conditional statement, I often encourage them at least to consider what the contrapositive is. Sometimes it's helpful; sometimes it's not; but it's never a bad idea just to run over it, especially as it has the added benefit of solidifying your understanding of the conditional reasoning involved.

I hope this helps!

[Verabriseis]

I don’t understand how answer choice B was diagrammed. I thought according to lesson 6 in the LR Bible pg 187 the unless phrase is kept the same and put in the necessary and the other portion is negated and made Sufficient. PLEASE explain, I’m so confused

[Jeremy Press]

Hi Verabriseis,

Good question! The original post's diagram of the "unless" statement (the first sentence) in answer choice B is a diagram of the contrapositive of what you would diagram using the PowerScore method outlined in Lesson 6 of the Logical Reasoning Bible.

Under the PowerScore method, you're absolutely correct that what is modified by unless becomes the necessary condition, and the remaining condition is negated and then diagrammed as the sufficient condition. Using that method, what you would diagram for the "unless" statement in answer choice B is:

Flights Reduced Higher Airfares

The contrapositive of that (which is always necessarily entailed in any conditional relationship) is the diagram given in the original post's explanation of the question.

The reason the original post diagrammed the contrapositive (rather than what the PowerScore method would initially produce) is that the subsequent premise and conclusion in answer choice B are built from a valid application of the contrapositive. It's easier to see that the premise and conclusion in answer choice B are valid if you diagram the contrapositive, in addition to what the PowerScore method recommends.

I hope this helps!

Jeremy

[Verabriseis]

Is there an indicator or way of knowing that I should apply the contrapositive to a choice? Bc I just diagrammed the answer choice and immediately crossed it off thinking it was incorrect. Are we supposed to apply the contrapositive to every choice each time? I feel like that’s a waste of time but is the reason I missed this question

[Jeremy Press]

Hi Verabriseis,

You don't necessarily have to diagram the contrapositive of every conditional relationship you diagram, if you can make the appropriate assessment of the answer choice from the diagram you created. In this case, I'm guessing you drew your (correct) original diagram of the unless statement, compared it to the premise and conclusion stated in the rest of answer choice B, and saw that there was no way answer choice B was making the same "Mistaken Negation" mistake as was present in the stimulus. If that's the case, then you did what you needed to do and you didn't need to diagram the contrapositive. If you rejected answer choice B for some other reason, then you got lucky on this question and you might want to consider diagramming the contrapositive in a similar future situation.

I hope this helps!

Jeremy

[annabelle.swift]

Hi! I got a different diagram for E than the Administrator. I got

dress code changed principal
      OR
2/3 of parent council

[annabelle.swift]

Oops sorry I hit submit too quickly! Anyway, for E, I got a different diagram than the administrator. I got

Premise: dress code changed    principal approve  OR  2/3 of parent council approve
Conclusion: principal approve     dress code changed

and that the correct contrapositive of the premise would be

principal approve  AND  2/3 of parent council approve     dress code changed

Is my diagram incorrect? Thanks