Logical reasoning PrepTest 112 · Section 4 · Question 19

Question prompt

Birds need so much Remaining source text redacted.
Why the credited answer is right

Credited answer: C

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

Stimulus Summary

Nectar provides more energy than seeds
Therefore - For birds with the same energy requirements, seed-eating birds take more time eating than nectar-eating birds

Answer Anticipation

This argument relies crucially on a common type of logic on the LSAT - comparative logic. It talks about the relative energy amount in nectar and seeds, and then it reaches a conclusion that compares the time spent eating between birds that eat nectar vs. those that eat seeds. Since we’re dealing with comparisons here, we should focus on whether the comparisons are supported.
So let’s dig into the conclusion. The first thing to note here is that it compares birds with “the same overall energy requirement,” so it’s controlling for the amount of energy needed. This is important in eliminating trap answers - anything that talks about different energy requirements will be wrong since the argument already accounted for it.
Moving on from there, it compares seed-eating birds and nectar-eating birds on the metric of time spent eating. Do the premises support a conclusion about the amount of time spent eating? They don’t - they don’t mention time at all!
Instead, they compare how much energy an equivalent amount of seed and nectar provides. The argument, thus, assumes that since nectar provides more energy per amount, that birds eating it spend less time eating.
But that’s assuming a connection between the energy per amount of the food eaten and the time taken to eat it! It’s possible that eating a given amount of seed takes a lot less time than the same amount of nectar. If, say, there’s only 1-2 drops of nectar per flower, it may take a lot of time to get enough drops to equal a couple seeds.
This argument assumes that the types of food take about the same amount of time to consume the same amount, so let’s find an answer highlighting that.

Answer choices

  1. A
    Birds of different species Remaining source text redacted.
    Why choice A is not credited
    The conclusion compares birds that do have the same energy requirements as each other, so the fact that this is rare is out of scope.
  2. B
    The nectar–eating bird does Remaining source text redacted.
    Why choice B is not credited
    As long as the birds are primarily eating nectar or seeds, then it doesn’t matter if they sometimes eat another type. This type of answer - one that blurs the lines between the groups - is almost always wrong on the exam.
  3. C
    The time it takes Remaining source text redacted.
    Why choice C matches the stem
    This answer compares the amount of time it takes the different birds to eat the different types of food, so it lines up with the gap in the argument. If the nectar-eating bird does take longer to eat the same amount as a seed-eating bird, then it may take that bird longer to eat enough even though there’s more energy in the nectar. This answer, therefore, is a necessary premise.
  4. D
    The seed–eating bird does Remaining source text redacted.
    Why choice D is not credited
    The conclusion limits itself to comparing birds with the same energy requirements, so body temperature (inasmuch as it’s related to energy requirements) is already accounted for, and this answer isn’t necessary.
  5. E
    The overall energy requirements Remaining source text redacted.
    Why choice E is not credited
    Another answer that deals with energy requirements! As we’ve said before, the conclusion controls for energy requirements by comparing birds that have equivalent ones, so this answer isn’t necessary for the argument to work.

What this tests

Question analytics

Based on historical answer selection rates for this question.

Answer choice distribution

  1. A 7%
  2. B 5%
  3. C Credited 68%
  4. D 11%
  5. E 10%

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