Logical ReasoningDifficulty: Hard

PT13 S2 Q24 Explanation

A certain airport security scanner

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

TopicsFlaw

Keep going in LSAT Lab

  • 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

Free to start

Full official LSAT questions are available through LawHub. This page provides LSAT Lab's explanation, strategy, and review tools without republishing the full official question.

Stimulus

A certain airport security scanner designed to detect explosives in luggage will alert the scanner’s operator whenever the piece of luggage passing under the scanner contains an explosive. The scanner will erroneously alert the operator for only one percent of the pieces of luggage of a hundred alerts explosives will actually be present.

What this question is testing

Flaw

Your task

Describe the reasoning error the argument actually commits.

Common trap

Answers that name a real logical flaw the argument doesn't actually make.

Winning move

Articulate the gap in the reasoning yourself, then match it to the choice that describes that gap.

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

The question
24.

The reasoning in the argument is flawed because

Answer choices

  1. Trap23% picked this

    ignores the possibility of the scanner’s failing to signal an alert when the luggage does

  2. Trap4% picked this

    draws a general conclusion about reliability on the basis of a sample that is likely

  3. Trap4% picked this

    ignores the possibility of human error on the part of the scanner’s operator once the scanner has

  4. Trap6% picked this

    fails to acknowledge the possibility that the scanner will not be equally sensitive to all

  5. Correct64% picked this

    substitutes one group for a different group in the statement of

    Why this is right

    As an addendum to that video, here's what we think this answer was trying to say. The 2nd sentence is saying, "when there is a bag with no bomb, only 1% of the time will the alert go off." The conclusion is saying, "when alerts go off, only 1% of the time will it be a bag with no bomb."

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

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