Logical Reasoning

PT119 · S3 · Q6 Heavy salting of Albritten’s roads

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Heavy salting of Albritten’s roads to melt winter ice and snow began about 20 years ago.

Conclusion

Continuing the salting of Albritten's roads at its present rate will render Albritten's groundwater unpalatable within the next few decades.

Evidence (since)

Salting Albritten's roads began 20 years ago. The groundwater now contains ~100mg of salt / Liter.

By comparison, in a less highly urbanized area where traffic patterns resemble Albritten of 20 years ago, the groundwater contains 10mg of salt / Liter.

Water that contains 250 or more mg of salt / Liter tastes unacceptably salty.

Evaluate

The author is presenting an Asymmetric Comparison (i.e. a Curious Fact) and making a causal assumption about it, so we can activate our Explain Curious Fact mindset.

Curious Fact ... how come A's groundwater is 100mg / L whereas the groundwater in this other area where salt isn't used much is only 10mg / L?

Author's Explanation ... the heavy salting of A's roads has increased its groundwater to 100mg.

We could weaken this argument by posing an Alternate Explanation for the 100 vs. 10 difference (maybe Albritten has more factories whose byproducts salt into the groundwater), or by attacking the plausibility of the idea that heavily salting the roads eventually adds salt to the groundwater.

But this argument also contains a prediction. The author is thinking that our current salting rate will get us from 100mg / L to 250mg / L in the new few decades.

The author is thinking,

We could hurt the argument by trying to throw a wrench into this prediction. Maybe the way salting roads contributes to salty groundwater isn't linear like that. Maybe at a certain point, salt clogs up the ground in such a way that additional salt doesn't leech down into the groundwater at as fast a rate (i.e. so maybe we'll eventually get to 250mg, but not in the next few decades).

Which one of the following, if true, most seriously weakens the argument?

Even water that contains up
Out of Scope: safe
The conclusion is saying that the water will be unpalatable (gross-tasting). It isn't saying the water will be unsafe to drink, so we can't weaken the argument by saying, "Even at 250mg, it'll still be safe."
10% picked this
The concentration of dissolved salt
Strengthens
This answer more or less proves the conclusion true. Within a few decades the groundwater will be 400 mg / L. As soon as you hit 250+ mg / L, you get unacceptably salty water, so within a few decades we will indeed have unpalatable groundwater in Albritten.
1% picked this
Salting icy roads is the
No Impact
Whether salting icy roads is the simplest way, the 2nd simplest, the 14th simplest way doesn't matter. We're not debating whether or not we should salt the icy roads. This type of answer is trying to get students to 'hear' an additional conclusion. Actual conclusion: if we continue to salt at our present rate, in a few decades the groundwater will be unpalatably salty. Students hear additional conclusion: we should stop salting at our present rate That latter, imagined conclusion is a much broader claim that has to take into account all the positives and negatives of salting. For that conclusion, we would weaken by saying, "Sure, author, salting the road will make the groundwater salty, but remember it is the simplest way to prevent accidents, so it's worth the tradeoffs!" But we can only weaken the actual argument by arguing that in a few decades, even if we continue to salt at the current rate, the groundwater won't be unacceptably salty.
1% picked this
Correct
Albritten’s groundwater contained roughly 90
Why this is right
If 20 years ago the groundwater was 90mg/L, and 20 years of salting has brought it to 100mg/L, then salting roads at the current rate adds about 10mg/L every 20 years, or 5 mg/L every 10 years. Thus, a few more decades (30 years) would add another 15 mg/L to the groundwater, taking us up to 115 mg/L. The author is claiming in his conclusion that within 30 years, we'll have already passed by that 250 mg/L threshold for saltiness, but it looks like at the rate we're going, it would take 300 years to add another 150 mg/L to the groundwater. If this chart helps us visualize .... 20 yrs ago 90 mg Now 100 mg 20 yrs from now 110 mg 40 yrs from now 120 mg 60 yrs from now 130 mg etc. The author got himself confused by comparing the 100 mg/L level in Albritten to the 10 mg/L level in the nearby town. He started thinking that "prior to salting, Albritten was at that 10mg/L level". This answer destroys that assumption. It's saying, "Nope, prior to salting, Albritten was at 90 mg/L". So this is weakening by making the prediction in the conclusion sound way off. At our current rate, we won't hit unpalatable saltiness for about 300 years, not "within the next few decades".
Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.
74% picked this
Salting of Albritten’s roads is
Irrelevant / Attacking the Trigger
This conclusion is making a prediction about a world in which we continue salting at our present rate. The only way to argue with such a conclusion is to say, "Nuh-uh ... in a world where we continue salting at our present rate, your prediction would NOT be true". We can think of this conclusion as a Conditional Conclusion: If we keep salting ? then within a few decades at the present rate unpalatable groundwater We can never strengthen a conditional conclusion by making the trigger seem more likely nor weaken a conditional conclusion by making the trigger seem less likely. We are assuming the trigger no matter what and trying to strengthen or weaken that the outcome would actually follow. If I say, "If Donald Trump ran for Prime Minister of Canada, he would win", you can't argue with me by saying, "He's ineligible to run for Prime Minister / he's not interested in governing Canada". You can only argue with me by accepting the hypothetical trigger and telling me how he would fail to win the Canadian election for Prime Minister.
14% picked this

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