Logical reasoning PrepTest 111 · Section 3 · Question 22

Question prompt

The folktale that claims 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

Argument

Valid or Flawed

Flawed

Question Type

Strengthen with Necessary Premise Questions / Sufficient & Necessary Questions

Stimulus Summary

Folktale, wrong, etc…
If rattlesnake tails didn’t break off:
A rattlesnake tail forms a new section each time it molts, so you can tell a rattlesnakes age by counting up the sections.

Answer Anticipation

There’s a really important feature of this argument that lets us streamline our Summary. It starts by highlighting a folktale that is wrong, but only for a certain reason. It then conditions its conclusion on that reason no longer applying - if a rattlesnake tail wasn’t so brittle, then…
By predicating the conclusion on the truth of that statement, we can more or less start our work there, as it’s a self-contained argument that lives in a world separate from the one where the folktale has problems. So the argument is trying to prove, in a world where rattlesnake tails didn’t break off, you can count up the segments to get their age.
Why does it believe this would be possible (again, if the tails didn’t break off)? Because a new section forms each time a rattlesnake molts. So where’s the gap in the logic?
Let’s approach this from another angle. Let’s suppose you knew that a rattlesnake tail formed a new section each time it molted, and you counted the sections on a snake to see there were 5 sections. What would you conclude? That it molted 5 times. However, that doesn’t tell you the age of the rattlesnake, unless there’s a connection between molting and age.
So what’s this argument assuming? That the rattlesnake molts at regular intervals, and thus counting up the segments will let you figure out how old it is. Let’s find an answer establishing that.

Answer choices

  1. A
    Rattlesnakes molt exactly once Remaining source text redacted.
    Why choice A is not credited
    This is a great...trap answer! Everyone loves this answer. After all, if a rattlesnake molts once a year, then counting up the segments will tell you its age. So what’s wrong with it? The rate doesn’t have to be once a year for you to be able to tell the age. Let’s say the rattlesnake actually molts once every six months - that would still let you count up the segments and figure out the age (just divide by two to get it in years). This answer is a sufficient premise, but it’s too specific to be necessary, as there are multiple molting rates that would still allow you to determine age.
  2. B
    The rattles of rattlesnakes Remaining source text redacted.
    Why choice B is not credited
    They don’t need to be identical in appearance. It just needs to be possible to count up the number of sections, which could be done even if the rattles look a bit different from each other.
  3. C
    Rattlesnakes molt more frequently Remaining source text redacted.
    Why choice C is not credited
    This answer establishes that molting happens at irregular intervals, weakening the argument. After all, if the molting happens at different rates throughout life, it’d be hard to translate that into an age just by counting them up.
  4. D
    The brittleness of a Remaining source text redacted.
    Why choice D is not credited
    The argument is conditioned on the rattles not being brittle, so this answer is out of scope. Also, the argument is about age, not life expectancy of the snake, making it doubly out of scope.
  5. E
    Rattlesnakes molt as often Remaining source text redacted.
    Why choice E matches the stem
    This answer establishes that at least one factor doesn’t change the rate at which rattlesnakes molt, which is a necessary premise for that rate being stable enough to determine age from it. If rattlesnake molting does change frequency when there isn’t food around, then it’d be impossible to determine age just by counting up sections. This answer is thus a necessary premise and correct.

What this tests

Question analytics

Based on historical answer selection rates for this question.

Answer choice distribution

  1. A 28%
  2. B 2%
  3. C 4%
  4. D 15%
  5. E Credited 51%

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