Logical ReasoningDifficulty: Easy

PT109 S1 Q25 Explanation

The number of airplanes equipped

A free, expert breakdown of this official LSAT Logical Reasoning question.

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Stimulus

The number of airplanes equipped with a new anticollision device has increased steadily during the past two years. During the same period, it has become increasingly common for key information about an airplane’s altitude and speed to disappear suddenly from air traffic controllers’ screens. The new anticollision device, which is therefore responsible for the sudden disappearance of key information.

What this question is testing

Weaken

Your task

Find the choice that makes the argument's conclusion less likely to be true.

Common trap

Answers that look negative but attack a claim the argument never relied on.

Winning move

Find the assumption the argument depends on, then pick the choice that undermines it.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
25.

Which one of the following, if true, most seriously weakens

Answer choices

  1. No Impact2% picked this

    The new anticollision device has already prevented a considerable number of

    The fact that the device prevents collisions doesn't affect whether it causes disappearance of key information from screens.

  2. No Impact4% picked this

    It was not until the new anticollision device was introduced that key information first began disappearing

    If key information began disappearing only after the device was introduced, it supports the idea that the device could be involved, not weakens it.

  3. No Impact1% picked this

    The new anticollision device is scheduled to be moved to a different frequency within the next

    This choice describes a plan to change frequency, but it does not address the current causal relationship claimed in the argument.

  4. Correct92% picked this

    Key information began disappearing from controllers’ screens three months before the new anticollision device

    Why this is right

    If key information began disappearing from controllers' screens three months before the device was first tested, it suggests the device is not the cause of this issue. This provides an alternate explanation for the disappearance, thereby weakening the conclusion.

    Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.

  5. No Impact2% picked this

    The sudden disappearance of key information from controllers’ screens has occurred only at

    This choice specifies where the problem occurs but doesn't impact the causal connection being made between the device and the disappearance of key information.

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