Logical Reasoning

PT21 · S3 · Q19 In the first decade following the

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In the first decade following the founding of the British Labour party, the number of people regularly voting for Labour increased fivefold.

Conclusion

The claim that is clearly false.

(i.e. the Labour party did not gain more voters in the 2nd decade than in the 1st)

Evidence

In the first decade since the founding of the Labour party, the number of people regularly voting for Labour increased fivefold.

In the second decade, the increase was the same (i.e. in the second decade it also increased fivefold).

Evaluate

The author thinks that the increase from 0-10yrs is the same as the increase from 10-20yrs, since they were both "a fivefold increase". Thus, he thinks, it's not the case that the increase during yr 10 and yr 20 was bigger.

But we can easily prove this wrong if we consider any numbers.

Let's say the Labour part started with 100 voters.

(fivefold ↑) (fivefold ↑) 0 yr 10 yrs 20 yrs

Voters 100 500 2500

Voters +400 +2000 added

This argument features a famous Percent vs. Number type shift. The evidence is percentage / relative / proportional. It's saying that each decade ended up 500% of where it started.

But the conclusion is about Numbers, because it's assessing the claim of whether the gained more voters during the first decade or the second.

Goal

Look for an answer explaining this math confusion. The premises flat out contradict the conclusion, since the increase from year 10 to year 20 is definitely bigger than the increase from year 0 to year 10.

19.

The reasoning in the argument is flawed because the argument

  1. fails to specify dates necessary

    Dates Not Needed

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

    3% picked this

  2. Correct

    draws a conclusion that cannot

    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.

    65% picked this

  3. relies on statistical evidence that,

    Not Irrelevant

    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.

    10% picked this

  4. fails to allow for the

    Not an Objection

    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.

    3% picked this

  5. overlooks the possibility that more

    Not an Objection

    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.

    19% picked this

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