Logical Reasoning

PT155 · S1 · Q6 The government's tax collection agency

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In a counterattack on the harmful effects of acid rain, wildlife experts are adding lime to the water of some lakes.

Statements

causal (neutralizes / staves)

Add lime ⇢ Neutralizes ⇢ Avoids some damage to lakes acid and restores some health

conditionals (must, if)

Lime used → Treated periodically w/ more lime in lake (b/c new water carries away lime)

Lake's water replaced → too expensive for more than once / 6 mos liming to be option

Evaluate / Goal

Since this is a (rare) Must Be True EXCEPT and there are four derivable inferences, it feels less advisable to work with these facts up front and try to figure out what can be derived. We're unlikely to figure out all four correct answers ahead of time, so let's head to the answers and find provable stuff.

6.

If all the statements above are true, each of the following must also be true except:

  1. If a lake is a

    Must Be True

    This is just the contrapositive of the final sentence. Lake's water replaced ? too expensive to be more than once / 6 mos candidate for liming Contrapositive: a candidate for liming ? lake's water replaced 6 months or longer

    9% picked this

  2. In some lakes, if liming

    Must Be True

    To be honest, this feels a little more like a strong Most Supported answer. We know that liming is used to counteract the harmful effects of acid rain. The passage doesn't exactly define what "successful counteraction" consists of. If I put in a handful of lime and it slightly staves off some damage and slightly restores the health of the lake, was that successful? But if we use a little common sense, assuming that acid rain is an ongoing phenomenon, then counteracting it with liming needs to be an ongoing phenomenon, because the 3rd sentence tells us that lakes get their water replaced over time, so the lime we add eventually disappears. That 3rd sentence is saying, "If you're going to use lime in a lake, then you must treat it periodically (i.e. add more lime periodically)."

    3% picked this

  3. Correct

    Unlimed lakes in which the

    Why this is right

    We can't prove anything about unlimed lakes because we never discussed them. We have no way to compare the harm acid rain will cause this lake vs. that lake. Some aspects of how much harm acid rain will cause in a lake will have to do with the specific wildlife that inhabits that lake. We could have a lake with higher levels of acid rain that is less harmed because there aren't as many sensitive organisms living in that lake. We might be thinking, "Isn't it just common sense that the more you replace the water, the better off you'd be? You're washing away the acid rain!" Yes, unless the water that's replacing the water in the lake is acid rain! Where does the water come from that replaces lakes? It comes from rain and from snow melt from nearby mountains. If that region experiences acid rain, then both the rain and the snow melt that are replacing the lake's water are made at least in part of acid rain.

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

    81% picked this

  4. Liming can be effective even

    Must Be True

    The second sentence allows us to derive this, because it says that liming "restores the health of some lakes where life has already been harmed by acidification." This is also a very weakly worded claim, which makes it easier to prove true.

    4% picked this

  5. If a lake's water is

    Must be True

    This is just restating what we get from the last sentence. The conditional is telling us that if a lake's water has to be replaced "too often / too frequently" (more than once every 6 months), then the cost of periodically re-treating with lime would be too high for that lake to be a candidate for liming.

    3% picked this

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