Logical reasoning PrepTest 130 · Section 4 · Question 11

Incorrect. As long as the Researcher was able to capture a large enough sample to be representative, it doesn't matter if that sample included almost all or just many armadillos, so it's not necessary for the argument that "few" armadillos were able to avoid tagging.

Incorrect. This answer deals with the second flaw we noted and anticipated as potentially leading to a correct answer—the sampling flaw. However, in stating that most armadillos weren't recaptured, this answer suggests that the recaptured armadillos might not be representative, thus undermining the argument, so we can rule it out.

Incorrect. If a few of the armadillos were killed by predators, sufficient information could still potentially be drawn from the remaining ones to draw a valid conclusion. Only if the predators killed so many armadillos that a valid sample was no longer available would this answer be relevant.

Incorrect. Even if the tags can be removed by the armadillos, that doesn't mean that they would be, and it definitely doesn't establish that they'd be removed in such a way as to call the sample into question.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Necessary Premise

Stimulus Summary:
Last year: Armadillos were captured and tagged in one area
This year: Tagged armadillos were recaptured, with most being within 100yds of where they were first captured
Conclusion: Armadillos are slow to move to other areas

Answer Anticipation:
The Researcher's conclusion here is an explanation of a phenomenon—an attempt to explain why her recaptured armadillos were found in almost the exact same place they were captured a year ago. Whenever an argument's conclusion is an explanation of a phenomenon, your first thought should always be of alternative explanations.

Here, the explanation is that armadillos don't move much. In order for that conclusion to hold, then all alternative explanations must be false. In this Strengthen with Necessary Premise question, therefore, one potential category of correct answer will rule out one of these alternatives. We could brainstorm some, but knowing that we're looking for that and not brainstorming can help us stay flexible.

One more thing we should consider before we head to the answers—this argument relies on a study that has a sample of armadillos. As with all studies featuring a sample, the argument assumes that sample to be large and representative. In particular here, the recaptured sample may not be representative of armadillos as a whole—maybe the Researcher only recaptured 10% of the armadillos. Another avenue for correct answers would address this—ruling out ways that the sample could be unrepresentative.

Answer Explanation:
This answer choice rules out a possible alternative that the argument fails to consider—mainly, that the armadillos aren't slow to move, they actually all moved out and then moved back! If armadillos migrate over the year, then the Researcher's data would still hold without the conclusion being valid, so this answer is necessary for the argument in that it rules out a competing explanation.

Key Takeaway:
Arguments that conclude a specific explanation for a phenomenon frequently ignore alternative explanations/hypotheses/theories. These arguments can be strengthened by ruling out these alternative explanations, and Strengthen with Necessary Premise questions will frequently have correct answers that rule out one of these alternatives.