PrepTest 106

[lcid:3520] Prep Test 106 LSAT — Logical Reasoning — S1 Logical reasoning

Question prompt

People who say that Remaining source text redacted.
Why the credited answer is right

Credited answer: B

The notes below walk through why it fits the stem and how to eliminate the rest.

Argument or Facts

Argument

Valid or Flawed

Flawed

Question Type

Strengthen with Necessary Premise Questions / Sufficient & Necessary Questions

Stimulus Summary

Flat land → Soil erosion from water isn’t a problem
Flat land → ~Build terraces to prevent erosion
Dooney County - Build terraces
Therefore - Dooney County isn’t flat

Answer Anticipation

The stimulus here is interesting in that it has two conditional premises that have the same sufficient condition, making it unclear how they work together. As such, we should start with the conclusion and work backwards to see what builds into it!
Here, the conclusion is that people who say Dooney County is flat are wrong - in other words, it’s not flat. (Always rephrase these conclusions about a view being wrong/mistaken to say what they mean!)
What do we know about Dooney County? We know that the farmers there build terraces. That connects to the second conditional premise, but that conditional had not building terraces as a necessary condition. So let’s take the contrapositive to get it to line up with the premise and conclusion:
Build terraces to prevent erosion → ~Flat land
So according to the second premise, if farmers build terraces to prevent erosion, then we can conclude that Dooney County isn’t flat. However, all we know is that they build terraces - not that they do so to prevent erosion! The argument is assuming the reason those terraces are built is to prevent erosion, so let’s find an answer stating that.

Answer choices

  1. A
    the only cause of Remaining source text redacted.
    Why choice A is not credited
    That first premise ended up being irrelevant to the argument, so this answer is out of scope. Even if we consider that first statement, it talks about “soil erosion by water,” suggesting that there are other causes of soil erosion.
  2. B
    there are terraces on Remaining source text redacted.
    Why choice B matches the stem
    This answer establishes that the Dooney terraces are built to prevent soil erosion, thus ensuring that they trigger the conditional premise and allow the conclusion to be drawn. If there are no terraces built to prevent soil erosion, then the terraces can’t trigger that conditional, preventing the conclusion from being drawn. This answer is thus a necessary premise.
  3. C
    terraces of the kind Remaining source text redacted.
    Why choice C is not credited
    The conditional premise is about the motive behind the terraces, not the effect. Even if those terraces can prevent soil erosion doesn’t mean that they were built for that purpose!
  4. D
    on flat land there Remaining source text redacted.
    Why choice D is not credited
    The stimulus establishes that soil erosion by water isn’t a problem on flat land, not that it isn’t a problem at all. Even then, we already discussed how that premise was irrelevant to the conclusion.
  5. E
    the only terraces in Remaining source text redacted.
    Why choice E is not credited
    The relevant premises are about terraces on farmland, so terraces elsewhere are out of scope.

What this tests

Discussion

  • B and C 2 replies

    Started by RitaW

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