Logical Reasoning

PT141 · S4 · Q8 Fluoride enters a region's groundwater

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Fluoride enters a region's groundwater when rain dissolves fluoride-bearing minerals in the soil.

Findings

causal/conditional (when)

Rain dissolves fluoride enters minerals w/ → groundwater fluoride in soil

correlation

higher fluoride || higher sodium concentrations in soil in soil

Evaluate

There are only two claims -- how can we synthesize them? Is there any Overlapping Ingredient?

They both talk about rainfall, fluoride-bearing minerals, and fluoride in the groundwater.

We know that rain + FL minerals = fluoride in the groundwater, but this final sentence seems to be telling us that how much fluoride makes it to the groundwater is heavily contingent on sodium.

For a given amount of rain onto a given amount of fluoride-bearing minerals, there ends up being more fluoride in the groundwater where there's more sodium.

Is the sodium somehow helping the rain dissolve the fluoride so that it gets in the groundwater. Or is the sodium a byproduct of the fluoride running into the groundwater (or neither)?

Goal

It seems hard to predict a definitive inference from that correlation (because correlations, famously, can be explained different ways). Let's just look for the most supportable answer.

8.

Which one of the following can most reasonably be concluded on the basis of the researchers' findings?

  1. Fluoride-bearing minerals are not the

    Too Specific: primary

    We have no idea how many sources of fluoride there are, and which one is or isn't the primary source. This paragraph never compares sources of fluoride. This answer is probably trying to get people to think that the paragraph is saying that sodium is the primary source of fluoride, but sodium isn't even identified as a source of fluoride.

    6% picked this

  2. Rainfall does not affect fluoride

    Contradicted

    The first sentence says that rain can lead directly to fluoride entering the groundwater.

    3% picked this

  3. Sodium-bearing minerals dissolve at a

    Unknown Comparison: dissolve faster

    Nothing in this paragraph deals with comparative degrees of dissolving. We couldn't possibly divulge which element is a faster dissolver form this paragraph.

    3% picked this

  4. Correct

    Sodium in groundwater increases the

    Why this is right

    This, of course, is not a must be true, but this is one of the possible interpretations of the correlation in the final sentence. Given that rain + FL-bearing minerals = FL in groundwater and given that when you control for amount of rain and amount of FL-bearing minerals, the fluoride seems to make it into the groundwater at significantly higher rates when there is sodium present, it seems like the sodium does something to facilitate higher fluoride concentration. This answer is offering a plausible guess, based on the fact that when all other relevant variables are controlled for, higher sodium seems to mean higher fluoride in the groundwater.

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

    56% picked this

  5. Soil that contains high concentrations

    Out of Scope: sodium-bearing minerals

    We only talk about certain groundwater having lots of sodium. We don't have any information about soil with lots of sodium-bearing minerals.

    32% picked this

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