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#26460
Complete Question Explanation

Question #2: Parallel Flaw. The correct answer choice is (B).

Unlike Saint Bernards, Labrador retrievers bark a lot. So, if you cross a Lab with a Saint Bernard you’ll get a moderate barker. Uhm... sure! :-)

Just because you mixed two elements with opposite characteristics doesn’t mean that you will obtain a product that has both of these characteristics in equal measure (or, in this case, the average of these characteristics). Mixing Pine-Sol with bleach will not give you a moderately strong cleaner that also bleaches moderately well. (You’ll end up with a highly toxic chlorine gas instead). Think of this as a variation on the Error of Composition.

Answer choice (A): This answer choice fails the Premise Test. The premises in the original argument appealed to all dogs of either breed. By contrast, the second premise of this argument appeals only to some students. This difference is sufficient to eliminate answer choice (A) from consideration.

Answer choice (B): This is the correct answer choice. Just like in the original argument, we have two entities with opposing properties (toxic or not). Mixing the two entities allegedly results in a product that is “moderately toxic,” just like Rosa’s dogs are allegedly “moderate barkers.”

Answer choice (C): This answer choice is incorrect, because it contains valid reasoning: if all students at Hanson live in Green County and all students at Edwards live in Winn County, then it logically follows that some members of the Perry family go to Hanson, and some go to Edwards. Furthermore, this answer choice also fails to Match the Conclusion, because the conclusion in the stimulus is about the mixture of two things, not about the individual elements that comprise that mixture.

Answer choice (D): Just like answer choice (C), this one contains valid reasoning. If Bob has worked as both a trasncriptionist and as an engineer, then it logically follows that he knows both shorthand and calculus.

Answer choice (E): This may seem like an attractive answer choice, because the closet mixes two elements with opposite characteristics. However, unlike the original argument, this one does not conclude that the closet will have the average of these characteristics. For answer choice (E) to be correct, the conclusion should have stated that the dresses in this closet are just about average in quality. Furthermore, this argument contains a Mistaken Reversal: just because all of Kenisha’s dresses are well made doesn’t mean that a well-made dress necessarily belongs to Kenisha. Same thing with Connie. The original argument does not exhibit a conditional reasoning flaw.
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 Dave Killoran
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#63399
This problem was covered in detail in Episode 4 of the PowerScore LSAT PodCast, entitled How to Solve Parallel Reasoning Questions. The explanation can be found at the 54:11 mark here:

PowerScore Blog, with full timing notes

iTunes
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 teddykim100
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#98884
Hello, I've listened to the podcast that Dave linked as well as read the explanation above. I also drilled the books sections on Error of Composition

I don't have any trouble seeing the flaw and got this question right my first time going through it. What I do have trouble with though, is a step in my thinking process. I happened to take a genetics course which drilled in me the idea that a cross between two purebreds does NOT average out to a 50/50 mix, but can have many different and surprising results. As soon as I read this stimulus, this concept comprised my entire reasoning and approach to this question.

However, I have trouble following when it comes to the "abstract" logic here. If I remove this genetics background from my thought process, I have trouble seeing how this is "logically" wrong. If I have 100% of A mixed with 100% of B, would it not be reasonable to think that a mix of the two will result in 50 of both? Again, this is taking the question in its "abstract" form, and representing it in a symbolic way. I know this question is very simple but the fact that I personally cannot justify the answer choice on a question this simple bothers me even more.
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 teddykim100
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#98885
To elaborate on the above (sorry for the double), I guess what I have trouble with is I feel that I brought in outside information on this question with my approach. However, no question on this test should require that of me, and I would just like to know for the next question how to spot this flaw in abstract terms.
 Rachael Wilkenfeld
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#99041
Hi teddy,

You don't need to bring in the genetics here! The stimulus doesn't establish that any mix would be 50/50 so we can't assume it is. That's it. That's the flaw. In abstract terms, we might say something like the argument doesn't provide the percentages of each part of a mix, so we can't deduce the overall makeup of the mix. That's true of the chemicals too. We don't know how much of chemical A or chemical B is in the chemical mix. So we can't say it's 50/50.

Hope that helps!

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