Logical Reasoning

PT133 · S2 · Q20 Whoever murdered Jansen

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

  • Save & drill this skill — build targeted practice sets from questions like this one

  • Video walkthroughs — watch every question solved step by step

  • 81 official LSATs — as questions, timed sections & full-length tests

Start practicing free

Whoever murdered Jansen was undoubtedly in Jansen's office on the day of the murder, and both Samantha and Herbert were in Jansen's office on that day.

Evidence

Whoever murdered Jansen was M → O undoubtedly in Jansen's office on the day of the murder.

Both Samantha and Herbert were H → O in Jansen's office on that day. S → O

Herbert is not the murderer. M → ~H

Conclusion

Samantha must be the killer. M → S

Evaluate

The argument assumes that O → H or S Samantha and Herbert were the only ones in Jansen’s office on the day of the murder.

NOTE: There is a distracting H → FI or FO intermediate argument that ~FI + ~FO. establishes that Herbert is not ჻ ~H the murderer by way of fingerprints and footprints. This intermediate argument is valid.

20.

Which one of the following, if assumed, allows the conclusion that Samantha was the killer to be properly inferred?

  1. If there had been footprints

    Out of Scope - Term Shift

    With Herbert the rule states that if he had committed the murder, the police would have found either his fingerprints or his footprints. So for him the question of leaving fingerprints or footprints but the police not finding them isn’t a possibility. For Samantha, she would have avoided leaving fingerprints or footprints in the first place, so again the question isn’t a possibility.

    5% picked this

  2. Jansen's office was the scene

    Out of Scope

    The conditions are such that determining who murdered Jansen does not require knowing anything about where the murder occurred.

    4% picked this

  3. Correct

    No one but Herbert and

    Why this is right

    This makes Herbert and O → H or S Samantha the only people who could have killed Jansen, so when the argument rules Herbert, it can be inferred that it was Samantha who was the murderer.

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

    62% picked this

  4. The fingerprints found at the

    Weakens

    The fingerprints found could not have been Samantha’s. And they were not Herbert’s. So if they were not Jansen’s, the investigation should probably include another suspect.

    17% picked this

  5. The fingerprints found at the

    Inference

    If each claim in the argument S → FI + FO were true, then Samantha did S not leave any fingerprints or ჻ FI + FO footprints. So the fingerprints found by the police could not have been hers.

    12% picked this

Continue the review in LSAT Lab

Save this question, watch the video walkthrough, and drill similar questions in your LSAT Lab account.

Save and practice this skill
LSAT Lab

Turn this review into a targeted study plan.

Save this question, drill more like it, watch the video walkthrough, and track your progress in your LSAT Lab account.

Start practicing free