#23 - Most auto mechanics have extensive experience.

[Administrator]

Complete Question Explanation

Parallel Flaw—FL. The correct answer choice is (E)

Although this type of formal logic appears less frequently on the LSAT today than it has in the past, some questions still require you to understand it. The supplemental materials for Lesson 8, accessible via the Online Student Center, provide an extensive Virtual Module on formal logic, along with a downloadable chapter on the same topic.

This stimulus involves a problem with chain reasoning. The stimulus states that most auto mechanics have extensive experience, and since most auto mechanics with extensive experience understand electronic circuits, most auto mechanics understand electronic circuits. We can abstract the idea as follows: Because most people belonging to category A have trait B, and most people with trait B understand C, most A’s understand C. This chain does not work, and it is easier to explain with numbers. Let’s say there are 100 auto mechanics. The term “most” indicates more than half, so at least 51 auto mechanics have extensive experience. Of those 51, most understand electronic circuits, so at least 26 understand electronic circuits. The author draws the conclusion that most auto mechanics, or at least 51 auto mechanics, understand electronic circuits. As we could see from breaking down the argument, we do not know that at least 51 auto mechanics understand electronic circuits. The correct answer choice must parallel this structure. Remember that as soon as an answer choice is not parallel to the stimulus, we can eliminate it as incorrect.

We can “speed up” this process of elimination by recognizing that the correct answer choice must contain an argument with the following structure:

• Premise: A most B
  
  Premise: B most C
  
  Conclusion: A most C

Unless an answer choice contains two “most” statements in the premises and a “most” statement in the conclusion, it will be incorrect. This immediately shows that answer choices (A), (B), and (C) are incorrect.

Answer choice (A): This answer choice does not use terms that indicate “most,” such as “a majority:” While the term “most” is not required in the correct answer choice, the idea of a majority certainly is required as it is essential to understand the error made. Therefore, you should eliminate this answer choice after a very quick read of the answer choice.

Answer choice (B): Unlike answer choice (A), this answer choice uses the term “most.” The beginning of the answer choice matches the structure of the stimulus. Most birds in the area are migratory (have trait A). Most migratory birds leave by November (most of those with trait A do B). However, the conclusion of the argument varies, and states that “few” birds remain. Just because “most” birds leave, doesn’t mean that only “few” are left.

Answer choice (C): Though this answer choice includes the concept of “most,” it does not include a faulty chain of logic. It even contains some conditional ideas in the conclusion by stating that most drivers who are not interested in driving fast do not buy sports cars.

Answer choice (D): In order to really understand this answer choice, it is easiest to abstract it out to see if the argument is the same as in the stimulus. Most nature photographers find portrait photography boring. We can abstract that as most As find B. Most portrait photographers especially enjoy photographing dignitaries. Since portrait photographers are a new group, we would abstract that as most Cs enjoy D. This is not the same sort of chain relationship we had in the stimulus, and thus the argument is not parallel.

Answer choice (E): This is the correct answer choice. Most A (snow removal companies) run B (lawn-care companies in the summer). Most B hire C (more workers in the summer). Therefore Most A hire C. Abstracting the answer choice we find this answer choice matches the stimulus, and makes the same error in using the term “most.”

[jared.xu]

I had problems eliminating answer B. Would B be parallel to the stimulus, if it stated in its conclusion: "Hence, few common species of birds remain in this region during the winter?" I would like to make sure that the problem with B is the illicit shift from "common species of birds" to just "birds," and not the use of the word "few." Does "few common species of birds remain in this region during the winter" mean the same thing as "most common species of birds in this region have left this region." Would both allow B to be parallel to the stimulus? Thank you.

[Eric Ockert]

Perhaps a simpler way of looking at it is if the PREMISE read, "Most birds in this region are migratory", then the answer would be parallel. But you are right, "THE MOST COMMON SPECIES OF BIRDS in this region" does not match up with the conclusion, "FEW BIRDS". The premise is essentially saying "most SPECIES of birds", while the conclusion is essentially talking about "most birds have left this region".

And yes, you are right that the "few" is not the issue. That "few birds remain" could be translated as "most do not remain".

Hope that helps!

Eric

[EL16]

Hello,

In looking over the previous discussion posts for this question, I see that for answer choice B, the Administrator's post says that the conclusion of this answer choice ("FEW birds remain") CANNOT be equated with "MOST birds leave", and therefore this is the reason as to why B is the wrong answer choice.
However, in Eric's discussion post, it seems to say the opposite of this, and says that the use of "few" birds remaining in answer choice B CAN be equated with "most" birds leaving, and that the use of "few" in this conclusion is NOT the reason that this is the incorrect answer choice.

Could someone please clarify which post is correct? I want to make sure I understand the inferences we can and cannot make using words like few/most so that I can correctly apply them in future questions. If few birds remain, then does that imply that most birds leave? Or is this not the case?

Thanks,
Elana

[Adam Tyson]

I'm going to respectfully disagree with Eric on this point, Elana, and say that "few" is not the same as "not most". If there are five birds and most don't leave, there could be three remaining, and that still could be "few". That said, Eric's main point is correct - one major problem here is "most common species" is not the same as "most birds". The official explanation is also correct - "few" is not the same as "not most". Each of these problems is enough, by itself, to kill this answer choice.

Few is subjective - it cannot be easily calculated, if at all. Most is not subjective - it has mathematical certainty in that it is guaranteed to be more than half. "Few" probably isn't a majority in most cases, but it still could be, so don't go equating "few" with "not most". Unless, that is, there is no answer better than the one that does that, in which case it could still be the correct answer. We aren't looking for perfect answers, or "right" answers on this test, only the "best" answer of the five presented. So, sometimes, under certain circumstances, you might have to pick an answer where few is supported by not most and vice versa.

[EL16]

Thank you for the clarification, Adam!

[ieric01]

Hey guys,

I challenged myself to find what’s wrong with C). I’d love it if you can take a look at it. Thanks!

Here it goes:

= = =
The support says people who drive sports cars get the most speeding tickets….

The conclusion says most drivers who are not interested in driving fast do not buy sports cars…

But the support (or premise) doesn’t necessarily lead to the conclusion.

Why?

Nothing in the premise talks about drivers being interested in driving fast or not. Had the premise said “If you buy a sports car, then you’re interested in driving fast” the conclusion would have been correct since it’d be a valid contrapositive.

But as it stands, we can’t know with absolute certainty that someone who doesn’t like to drive fast won’t buy a sports car. Perhaps they would, because of the status that comes along with it.

[KelseyWoods]

Hi ieric01!

Good attempt! But your analysis is a bit off.

The conclusion here is actually that first sentence:
It's not surprising that Speeding tickets Sports Cars

Notice that the conclusion isn't just that most speeding tickets go to sports car drivers. The conclusion is actually that that fact is not surprising.

The premise, then, (to answer the question, why isn't that fact surprising?) is the last sentence:
Interested in driving fast Sports Cars

Notice that this is Formal Logic because of the use of "most" rather than the Conditional Logic that we see more often. Formal Logic is a bit different than Conditional Logic because it is not as absolute so you can't easily make contrapositive inferences.

I'd say the main flaw here (and many arguments have multiple flaws!) is that just because most people who don't like speeding don't buy sports cars, that doesn't necessarily mean that most people who speed are driving sports cars. Maybe it's true that there just aren't many people who buy sports cars in general and only like 5% of people who like speeding buy sports cars. If that's the case, you just wouldn't have many speeders or non-speeders buying sports cars and it really wouldn't explain why most of the speeding tickets go to sports cars. (Not to mention the fact that being "interested in driving fast" is not really the same as "speeding.") So basically, the fact that most people who are not interested in driving fast do not buy sports cars does not make the fact that most speeding tickets go to sports car drivers any more or less surprising.

Hope this helps!

Best,
Kelsey

[ieric01]

Kelsey that was a great explanation! Thank you a million