PT2.S2.Q11 - if the forest continues to disappear

TheBatmanTheBatman Alum Member
edited February 2018 in Logical Reasoning 255 karma

PT2.S2.Q11 LSAT 2 PREPTEST 2 Question 11 section 2

I don't get how this answer is "B."

The question is asking "Which following statements are consistent with biologist's claim, but not with politician's."

biologist claims: deforestation --> NO Koala

Politician claims: If save Koala --> stop deforestation (did I get that translation right?)

How is "B" consistent with Biologist's claim? I see how it's not consistent with politician's claim, which is part of the answer.

Is it that the Koala could still get extinct for another reason. If that's so, how do I get in the mind set to infer an answer like that?


  • Grace...Grace... Alum Member
    edited February 2018 339 karma

    B: Deforestration continues at its present pace --> koala approach extinction
    P: Stop deforestration --> Koala saved
    If you look at this sentence, "All that is needed to save the koala to stop deforestration," it's saying that if you stop deforestration, it is guaranteed that koala would be saved. So stop deforestration is sufficient condition.

    (B) is consistent with Biologist. Deforestration being stopped is failing sufficient condition of Biologist, so koala could approaching extinction or not approach extinction. Both are possible. (sufficient fails, rule becomes irrelevant) so deforestration stopped and koala becomes extinct is consistent with biologist's statement.

    However, It's inconsistent with the politician. If deforestration is stopped, koala must be saved, but (B) says koals becomes extinct, which is not possible. (sufficient condition satisfied, necessary condition must follow) That cannot be true and is inconsistent with politician's statement.

    If you think of "consistent with" as could be true, and "inconsistent with" as cannot be true, it may be little easier. So find a scenario that could be true with biologist's statement, and cannot be true with politician's statement.

    To solve this problem quickly, you can just look at what cannot be true with politician's statement first. If there are more than one, then narrow down to something that could be true with biologist's statement, but in this case, there is only one. So find the one that satisfies politician's sufficient condition and fails the necessary condition: stop deforestration, koala become extinct.

  • thisisspartathisissparta Alum Member
    edited February 2018 1363 karma

    Yeah, I think you got the translation of the second premise wrong. It says that "all that is needed to save the koala is to stop deforestation”. That is, stopping deforestation is sufficient to save the panda. In other words, if we stop deforestation, then the koala will be saved.

    Let's break it down in terms of lawgic:

    i) Continue to lose the forest -> Koala extinct
    Contrapositive: /Koala extinct -> /continue to deforest

    ii) Stop deforestation -> /Koala extinct

    For the biologist, saving the forest is a necessary condition to saving the koala, not a condition that assures it's survival. So, you can have the Koalas headed toward extinction, whilst still stopping deforestation.

    This isn't the case for the politician. If we stop deforestation, the koalas have to survive.

    (D) highlights just that.

  • TheBatmanTheBatman Alum Member
    255 karma


    THANK YOU! Got it.

  • Pretzel LogicPretzel Logic Monthly Member
    226 karma

    Wow, this was one of the toughest Q's I've come across. I found this thread the closest I'd get to understanding it.

    I misunderstood the politician's argument and this took a while to understand. Evidently "all that is needed..." is correctly understood as "all that is necessary...". "All that is necessary to save koala is stop deforestation. Stop D > Save K.

    This certainly helped to understand how (B) could be correct.

    But for the Biologist, I struggled to grasp that the correct answer involved failing the sufficient and thus still being logically "ok".

  • leoxnardxleoxnardx Alum Member
    82 karma

    Ok I know this is like 4+ years ago but I was doing it and figured it out so I'll add on to the answer.

    The struggle was between B and D. Let's look at the passage. Basically the biologist is saying that IF deforestation continues at this rate (DC), the koala will approach extinction (AE). DC --> AE, contrapositive /AE --> /DC. In English is IF the koala does not approach extinction, continued deforestation must have stopped. Politician is saying that if we stop Deforestation, namely /DC, we can save the koala, /AE. in lawgic, this goes like /DC --> /AE.

    What is the difference here? the Politician takes what is necessary for the preservation of the koala as the sufficient. It can totally be true to /DC and still have AE, as other factors such as ppl poaching the koala leading to extinction. So what in the answer choice reflect that? Let's look at AC D first. Well this is not inconsistent with the politician's claim. The answer choice states that deforestation slowed, meaning deforestation did not continue at a rate, /DC, then the koala survives, /AE. In lawgic it's /DC-->/AE exactly what the politician is saying.

    Answer B however is inconsistent with the politician: deforestation stopped, /DC, but the koala still died out, AE. /DC --> AE. This makes the sufficient /DC no longer sufficient to stop the koala from extinction, contradicting the interpretation by the politicians

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