Logical reasoning PrepTest 119 · Section 4 · Question 8

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Sufficient Premise

Stimulus Summary:
Music major → In choir
Therefore - Live off campus → not Music major

Answer Anticipation:
Conditional logic shows up frequently in Strengthen with Sufficient Premise questions. When it does, we should work to get any conditional statements to line up with the conclusion, chain together what we can, and then find the missing piece.

Here, let's start with what we didn't diagram out—the opening line. The reason for this is that the conclusion is a conditional, and conditionals can't be supported by anything short of another conditional. A some statement will never be able to support a "none" conditional, so we can safely ignore it for the purposes of the logic of this question. All it's doing is establishing that some students do, in fact, live off campus. It's background.

With that noted, the premise here shares the term "Music major" with the conclusion, but it's in the wrong condition and negated, so we need to take the contrapositive of that premise:
not In choir → not Music major

From here, we can see that the missing piece of the argument will connect the new term in the conclusion to the sufficient condition of the premise. And since the new term is in the sufficient condition of the conclusion, that's where it should be in the answer, as well (or negated and in the necessary condition, as in the contrapositive):
Live off campus → not In choir
In choir → not Live off campus

Answer Explanation:
Live off campus → not In choir. This matches our anticipation and is the correct answer.

Key Takeaway:
When a Strengthen with Sufficient Premise question has conditional premises and a conditional conclusion, diagram everything out, take contrapositives until the terms match up, and then combine what you can. This should highlight where the missing piece is.

Incorrect. Music major → In choir. This answer restates the premise.

Incorrect. A Some statement can never justify a conditional conclusion, so we can eliminate this answer after the first word.

Incorrect. not Live off campus → Music major. Note the language here—it's about students who don't live off campus/live on campus. This is a partial negation of the conclusion, so it doesn't justify it! If this talked about students who did live off campus, it'd restate the conclusion, which would technically make it a correct answer, but that's not how these questions work and so you should be suspicious of any answer you think restates the conclusion.

Incorrect. In choir → Music major. This answer is the reversal of the premise. It would only be correct if the argument were flawed because of such an illegal reversal, but it's not—it's missing a piece—so this answer is incorrect.