Logical ReasoningDifficulty: Easy

PT142 S1 Q15 Explanation

Researcher: Salmonella bacteria are

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

TopicsParadox

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Stimulus

Researcher: Salmonella bacteria are a major cause of illness in humans who consume poultry. Young chicks that underwent a new treatment exhibited a lower incidence of Salmonella infection than did untreated chicks, although one week after the treatment was administered a variety of bacteria than did untreated chicks.

What this question is testing

Paradox

Paradox

The puzzle is this. Treated chicks have less Salmonella (good!) but a week later have higher concentrations of all kinds of bacteria. How can a treatment that reduces a specific bad bacterium also lead to overall higher bacterial loads?

Anticipate

The classic answer: the treatment populates the chicks with helpful or harmless bacteria that compete with Salmonella for resources — so the harmless bacteria thrive (driving up the total bacterial count) while Salmonella struggles to get a foothold.

Think of it like seeding a garden with grass to crowd out weeds. The total plant cover goes up, but the weed cover goes down. Same principle here.

Goal

Find an answer that says the bacteria found in the treated chicks are harmless and outcompete Salmonella.

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

The question
15.

Which one of the following, if true, most helps to explain the concentrations of bacteria one week

Answer choices

  1. No Distinction4% picked this

    The new treatment takes several weeks

    If the treatment takes weeks to administer, that doesn't explain why the chicks had higher bacteria after the treatment but lower Salmonella. The duration of the treatment doesn't address the puzzle.

  2. Cheats Paradox2% picked this

    Levels of Salmonella bacteria in young chicks are generally not high

    If Salmonella levels in young chicks are generally low to begin with, that might explain why treated chicks have low Salmonella, but it doesn't explain why they have higher total bacteria than untreated chicks. The puzzle is about the elevated bacteria count, which this answer ignores.

  3. No Distinction2% picked this

    Most chicks develop resistance to many harmful bacteria by the time

    This is about adult chicks developing resistance over time. The puzzle is about young, treated chicks measured a week after treatment. Adult resistance is irrelevant to this stage.

  4. Restates Paradox5% picked this

    The untreated chicks experienced a higher incidence of illness from infection by bacteria other than Salmonella

    This essentially extends the puzzle without explaining it. If untreated chicks had more illness from non-Salmonella bacteria too, that doesn't tell us why treated chicks had higher concentrations of various bacteria a week after treatment.

  5. Correct86% picked this

    The bacteria found in the treated chicks were nonvirulent types whose growth is inhibited

    Why this is right

    This explains both halves of the puzzle. The bacteria in the treated chicks are nonvirulent (so they don't cause illness), and they inhibit Salmonella growth (so Salmonella stays low). That explains why treated chicks have higher bacteria concentrations and lower Salmonella — the bacteria that flourished are harmless competitors that crowd out the harmful Salmonella.

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

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