PrepTest 109
[lcid:3532] Prep Test 109 LSAT — Logical Reasoning — S1
Logical reasoning
Question prompt
The number of airplanes
Remaining source text redacted.
Why the credited answer is right
Credited answer: D
The notes below walk through why it fits the stem and how to eliminate the rest.
Question Type
Cause & Effect / Weaken Questions
Answer choices
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AThe new anticollision device Remaining source text redacted.
Why choice A is not credited
Incorrect. The argument isn't about balancing the pros and cons of this device—it just wonders whether it's causing a specific phenomenon. As such, the number of collisions it has prevented is out of scope. -
BIt was not until Remaining source text redacted.
Why choice B is not credited
Incorrect. Causal statements are inherently causal—the cause has to happen before the effect, and close enough that they can be related. This answer establishes that that is the case—the devices being installed predate the information disappearing. That strengthens the argument, so this answer is incorrect. We'd need an answer establishing that the information was disappearing before the devices were installed. -
CThe new anticollision device Remaining source text redacted.
Why choice C is not credited
Incorrect. Without knowing why this is the case, we can't tie it into the argument about the devices causing the information disappearing. If anything, it seems as if a move to switch the frequencies—based on what the stimulus says about the devices and air traffic radars operating on the same frequencies—would suggest that it's believed the device is responsible for the problem here, which certainly doesn't weaken that argument. -
DKey information began disappearing Remaining source text redacted.
Why choice D matches the stem
Correct. Argument or Facts:
Argument
Valid or Flawed:
Flawed
Question Type:
Weaken
Stimulus Summary:
Past two years — The number of planes with a new device has increased
Past two years — Key information is increasingly disappearing from screens
Conclusion — The devices are responsible for the disappearing information
Answer Anticipation:
Claiming that one thing is "responsible" for another is claiming that it's causing the other. We know that correlation/causation flaws are common in Weaken questions so a causal conclusion should catch our attention! If we see it we should check the premises to see if they establish a correlation. Here they do—over a two—year period a device was installed in more and more planes and information disappeared with increasing regularity.
Since we have a correlation/causation flaw we should anticipate one of the common answers:
(1) Identify an alternative cause (something that would have led to both new devices being installed and information disappearing—e.g. solar flares maybe?)
(2) Counterexamples (places where the information is disappearing despite the planes not having the devices; places where the devices are installed but information isn't disappearing)
(3) Reversed causality (maybe the devices are being installed because no one can figure out why the information is disappearing from screens necessitating a technological solution to avoid crashes)
Answer Explanation:
This answer is the flip of (B). If the information was disappearing before the devices were installed then the devices can't have caused at least those initial cases of disappearing information weakening the argument. This is a variation of the counterexample answer choice—it shows a situation where the effect was present without the cause.
Key Takeaway:
Causality has an inherent timeline element to it—the cause must show up before the effect. As such answers that play with the timeline are in scope and should be fully considered. -
EThe sudden disappearance of Remaining source text redacted.
Why choice E is not credited
Incorrect. Without tying those large airports to the devices, this answer is out of scope. If anything, though, this answer could align with the argument as, presumably, larger airports have more airplanes, and more airplanes would have more devices.
What this tests
Discussion
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Why is A wrong? 3 replies
Started by apablo
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Explain C please 2 replies
Started by Mazen
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explain please 2 replies
Started by djayasinghe