Logical ReasoningDifficulty: Hard

PT21 S3 Q19 Explanation

In the first decade following the

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

TopicsFlaw

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Stimulus

In the first decade following the founding of the British Labour party, the number of people regularly voting for Labour increased fivefold. The number of committed Labour voters increased a further fivefold during the party’s second decade. Since the increase was thus the same in the first as in the second decade, the party’s second decade than in its first is clearly false.

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
19.

The reasoning in the argument is flawed because

Answer choices

  1. Dates Not Needed3% picked this

    fails to specify dates necessary to evaluate the truth of the conclusion, even though the argument depends on

    We don't need dates to evaluate this math. Initial State Time period 1 Time period 2 x 5x 25x

  2. Correct64% picked this

    draws a conclusion that cannot be true if all the data advanced in its

    Why this is right

    If it's true that each decade the number of voters increased fivefold, then the second decade definitely added more voters (5 times as many) than the first decade added. So if the premises are true than the conclusion cannot be true; it must be that more voters were added during the second decade.

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

  3. Not Irrelevant10% picked this

    relies on statistical evidence that, strictly speaking, is irrelevant to establishing

    Irrelevant is a really strong term that means the evidence as nothing to do with the conclusion. But, as our correct answer points out, the evidence established that the conclusion is false, so it can't be irrelevant.

  4. Not an Objection3% picked this

    fails to allow for the possibility that the policy positions advocated by the Labour party changed during

    Would it hurt the argument if the policy positions did change during the period in question? No, because this argument is only about math. It's not about explaining why the numbers went up, went down, or stayed the same. It's just about assessing whether they went up, went down, or stayed the same.

  5. Not an Objection19% picked this

    overlooks the possibility that more elections were held in one of the two decades than were

    The fact that this answer doesn't specify which of the two periods had more elections would mean that it is destined to have unclear impact. But it's not even clear it would have impact even if it specified which period had more elections. The number of committed Labour voters is the same, whether there are 50 elections during a decade or 15 elections. We're talking essentially about who is registered to vote for Labour.

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