PrepTest 101

[lcid:3501] Prep Test 101 LSAT — Logical Reasoning — S2 Logical reasoning

Question prompt

Not surprisingly, there are Remaining source text redacted.
Why the credited answer is right

Credited answer: E

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

Argument or Facts

Facts

Valid or Flawed

NA

Question Type

Must Be True Questions / Quantifiers Questions / Sufficient & Necessary Questions

Stimulus Summary

Professor → 18 or older ~18 or older → ~Vote Brilliant --some-- Professor Brilliant --some-- Vote Brilliant --some-- ~18 or older

Answer Anticipation

First, let’s make sure we understand how we got to our Summary. The first two statements are more difficult conditionals, using “no” as the indicator word, but you can apply a process to diagramming them out as we did. The bigger note here is making sure that you standardize the discussion of age. Whether you did this as Under 18 and ~Under 18, or 18 or older and ~18 or older, it’d be important that you represent them using the same terms since they represent negations of each other. Also important to note is that this doesn’t ignore 18-year-olds - they’re included in the 18 or older group (or the ~Under 18 group, as someone 18 isn’t under 8).
From there, we get three some statements, which are relatively straightforward to diagram.
With all that noted, we have two potential approaches. The first is to draw all the inferences we can by seeing what we can combine. The second is to “backsolve” and look at the answers, seeing which ones we can support. Here, there are a lot of potential combinations between the statements, so let’s backsolve.
(One thing we would note before moving on is that the conditionals don’t chain together - feel free to take the contrapositive of either to see that the shared term ends up on the same side of the arrow.)

Answer choices

  1. A
    No professors are eighteen–year–olds.
    Why choice A is not credited
    The premises only talk about those who are 18 or older (or under 18). While the former group includes people who are exactly 18, there’s no way to tell if anyone in that professor group is exactly that age.

  2. B
    All brilliant people are Remaining source text redacted.
    Why choice B is not credited
    There’s no way to know if the last three some statements build up to all brilliant people. Since each statement talks only about “some” brilliant people, between all three statements, it could be talking about, say, 3% of brilliant people!

  3. C
    Some legal voters are Remaining source text redacted.
    Why choice C is not credited
    To get the term “~Professor,” we’d need to take the contrapositive of statement #1. However, if we do that, we can’t combine it with the statement about legal voters (statement #4) since they don’t share a term. Ergo, we can’t infer this answer.

  4. D
    Some professors are neither Remaining source text redacted.
    Why choice D is not credited
    We know that some brilliant people are professors, but that doesn’t preclude all professors from being brilliant people, so this answer isn’t supported.

  5. E
    Some brilliant people are Remaining source text redacted.
    Why choice E matches the stem
    Some brilliant people are under 18, based on statement #5. Adding that to statement #2, we can say that some brilliant people can’t vote. Adding statement #5 to the contrapositive of statement #1 (~18 or older → ~Professor), we can say those same brilliant people aren’t professors. As such, there are some brilliant people who are neither professors nor legal voters (those brilliant people who are under 18). This answer is supported and is thus correct.

What this tests

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