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#15 - Rhonda will see the movie tomorrow afternoon only if

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Complete Question Explanation

Parallel Reasoning-SN. The correct answer choice is (B)

This stimulus is easier to understand if you pay attention to the formal logic content:


    Rhonda goes to movie ..... :arrow: ..... Paul goes to concert

    Paul goes to concert ..... :arrow: ..... Ted goes to concert

    Ted refuses to go to the concert


    Ted goes to the concert ..... :arrow: ..... Rhonda goes to the movie

The reasoning is logically valid, and involves the contrapositive of the additive inference.

Answer choice (A): This answer choice does not link the first element to the last, so is dissimilar. Furthermore, this choice involves a Mistaken Reversal of the premise:

    Janice visits ..... :arrow: ..... Janice finds baby-sitter

so this choice is logically flawed, and incorrect.

Answer choice (B): This is the correct answer choice. It can be diagrammed as:

    Gary does laundry ..... :arrow: ..... Peter has to work ..... :arrow: ..... Cathy is ill

    Cathy is ill ..... :arrow: ..... Gary does laundry

This illustrates that this response involves a correct additive inverse and uses the contrapositive, just as was done in the stimulus.

Answer choice (C): Since the first premise contains two sufficient conditions, this response fails the Premise Test, and is incorrect. You should immediately eliminate this choice.

Answer choice (D): Since the first premise contains a choice of necessary elements, and the stimulus did not, this response fails the Premise Test. Eliminate this choice immediately.

Answer choice (E): This response does not link the first and last elements. Also, this answer choice contains a Mistaken Reversal of

    Mark goes to the museum ..... :arrow: ..... Postponed appointments

so this choice contains fallacious reasoning, and is incorrect.
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After correctly identifying the structure of the reasoning in the stimulus, I immediately went thru and first eliminated any answer choice that didn't have 'unless' included. So after I quickly eliminated C D & E, I had just A & B left as my Contenders. I felt the use of 'unless' was important (enough) in matching up the answer choices... is that incorrect?? Is it not necessary as a part to compare when paralleling reasoning ??? Thanks.
Nikki Siclunov
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I'm afraid this is not a logically correct way to eliminate the incorrect answer choices here. You just lucked out :) The reason is simple: you should be looking for an answer choice that has the same conditional structure as the original argument, and the word "unless" can easily convey a conditional relationship of the type you're looking for. There are many ways of conveying the same exact set of conditional relationships, so don't just dismiss answers that use conditional indicators that differ from the ones used in the stimulus. This is not a material difference.

For more information on this issue, please consult the blog post I wrote not too long ago :)

Nikki Siclunov
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Nikki, thanks again. I just re-visited this question, and this time I:

1) Read thru the stimulus and quickly recognized the logic structure as A :arrow: B :arrow: C; conclusion: ~C :arrow: ~A (I didn't even have to write it out, like I usually would!).
2) I then quickly glanced at the conclusion of each answer choice to check if it matches with the negation of the stimulus' conclusion, leaving me with B & C as contenders
3) Then I read thru B, decided it was correct bc it matched up perfectly with my prephrase.
4) Read thru the entirety of C, saw that it was wrong, even from the first sentence.
5) Chose B as the correct answer.

It didn't even cross my mind that 'unless' had to be in the answer choice, just that the diagram had to be the same! That's encouraging that from the time I posted this (a month ago), I've since addressed that parallel reasoning question mis-approach.

Just want to make sure, though, that my first step in eliminating the answer choices with a conclusion that does not "match" the negation(/certainty) of the stimulus' conclusion is a good & accurate way to approach it?? I did that since the Course book recommends that as one of the first things to look for to help you quickly assign answer choices as losers or contenders. I do, however, feel like I remember reading that, if after you do that, your contenders don't seem to be correct, you should re-assess the answer choices you eliminated, bc there is still a (small) possibility it could be the right answer... so, if B or C didn't seem right, I would have looked back at A, D, & E. But since I was sure B was right, I felt good about that approach in this question. Look forward to your thoughts. Thanks !!
Claire Horan
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You restated the strategy correctly. You should eliminate answer choices that don't seem to match, but there is a small chance that you made a mistake in thinking a conclusion didn't match that did. It isn't so much that you should eliminate answer choices that don't have exactly the same wording, but rather the level of certainty, etc. needs to be the same. Good job!
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I got this question right, but I was confused about one of the wrong answer choices. On C, the explanation says that there are two necessary conditions. I thought there were two sufficient conditions because both "it doesn't rain" and the "market has fresh fist trout" are introduced by "if" which I thought was a sufficient indicator. Could you help me with this?
Jon Denning
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Hi mankariousc - thanks for the question!

You are correct about answer choice C: that should say two sufficient conditions, not two necessary conditions. So I'm going to edit the explanation provided to make that change :)

Good eye and thanks for letting us know! Keep up the hard work!
Jon Denning
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