Logical reasoning PrepTest 154 · Section 1 · Question 25

Incorrect. This answer choice makes a prediction about the future based on past events. However, it doesn't reverse the relationship as the stimulus does ("each tropical storm" is the sufficient condition indicator), instead negating it:

Previous tropical storm → Major hurricane
not Tropical storm, therefore not Major hurricane

Incorrect. This answer choice makes a prediction about the future based on past events, but it doesn't reverse the relationship as the stimulus does ("every spring thaw following . . . " is the sufficient indicator):

Previous spring thaw after high snowfall → Overflowed
Spring thaw after high snowfall, therefore overflow

Incorrect. This answer doesn't make a prediction about the future based on past events, instead drawing a conclusion about Earth based on other planets. It also doesn't reverse a relationship, treating rare minerals as establishing a period of meteor bombardment on both other planets and Earth.

Incorrect. This answer's first statement isn't establishing a relationship about what has happened in the past, but instead about what will always happen in response to a given event. As such, this answer doesn't have the same past vs. future flaw, nor does it feature an illegal reversal. In fact, this argument is valid!

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Flawed Parallel Reasoning

Stimulus Summary:
Previous major earthquakes in region → Preceded by minor tremors
There have recently been minor tremors, so there will soon be a major earthquake.

Answer Anticipation:
There are two issues here that we should be able to identify. First, the argument bases a prediction about the future based on trends that have been true in the past. However, there's no indication that the connection between tremors and earthquakes will continue to hold true. Second, in making that prediction, the argument reverses the logic from the stimulus. We know that all prior major earthquakes were preceded by minor tremors, but it could be the case that there have been many instances of minor tremors not followed by a major earthquake. The argument, however, ignores that possibility, so that's another flaw that must match.

Note that the argument doesn't ever state or assume that the tremors are causing the earthquakes, just that they're correlated with them, so any answer that concludes causality likely won't be correct, as it will likely introduce a correlation/causation flaw.

Answer Explanation:
This answer does make a prediction about the future based on all outbreaks of a disease that have happened "[s]o far." It also reverses the relationship:

Previous local outbreak of disease → Detection of high rate in wildlife
Detection of high rate in wildlife, therefore impending outbreak
This answer features both of the flaws from the stimulus, so it's the correct answer.

Key Takeaway:
First, predictions and conditionals are both common areas that go wrong in LSAT argument, so those two features of this stimulus should jump out at you. Second, be very careful with the conditionals here. The stimulus doesn't establish that earthquakes guarantee tremors, just that all prior earthquakes had tremors. That timeline aspect of the conditional (that it's talking about prior events) is very important to not falling for an answer such as (D), that creates an overarching conditional relationship instead of just talking about all known instances of a phenomenon.