PT 82 Logical Reasoning 1

Please note that this is the section that begins with a question about penalties for drinking alcohol in student housing. If you’re looking for the section that begins with a question about Otto offering Rhett a ride to work, then check PT 82 Logical Reasoning 2.

Question 11: Lalolah River

Question Type: FLAW

  • This means we should look for the conclusion, find the evidence, and then think through the problem in the argument.


  • Conclusion: The work that they are doing to clean up the Lalolah River must be working.
  • Evidence: Last year, the river was the most polluted out of the 15. Now it’s just the 3rd most polluted.
  • Other notes: Notice that the last sentence has both your conclusion and some of the evidence. Everything after the “since” is evidence.
  • Analysis: We just know that the Lalolah River’s rank improved, but we don’t have strong evidence about why. The conclusion claims that the reason for the change in rank is the measures taken to clean up the river, but there could be other reasons for the change in rank. (Maybe the other rivers got way more polluted, while the Lalolah River is still the same as it was before?) The trouble here is that we’re using data about rankings to support a conclusion about an actual pollution level. But notice that we don’t really know whether the river is more or less polluted than before. We just know that its rank is improved.

Answer choices:

  • A. In order for this to be right, the passage would have to say that because we don’t have evidence that one thing is true, that counts as evidence that something else is true instead. But we don’t really have an opposing claim here at all, so this answer isn’t right.
  • B. In order for this to be right, we’d have to see the term “most polluted” be used with two different definitions. For example, it might be used once to mean “has the most toxic stuff in it” and once to mean something else. (I’m struggling to think about what that would even be, except for in the sense of having a polluted mind — “has more dirty thoughts than other rivers.”) We don’t have two definitions at play here, so this isn’t right.
  • C. It’s true that we don’t know what the basis of the ranking was. Presumably something about pollution, but we don’t know the specifics. But it’s also not a problem that we don’t know this. Whether the ranking was based on the amount of pesticide runoff in the river or how much of a weird smell the river has is kind of irrelevant to the fact that whatever scale we’re using, the Lalolah River’s rank improved. So while this answer IS something that the argument does, it’s not a flaw and therefore not our answer.
  • D. In order for this answer to be right, the stimulus would have to talk about the pollution in the water district as a whole – something like an average pollution level. But the commission is ranking each river individually. The stimulus can’t confuse individual rivers with the water district as a whole if the water district as a whole is never mentioned. So this isn’t right.
  • E. CORRECT In order for this answer to be right, the stimulus would have to assume that a change in the rankings is equivalent to a change in the pollution level of the river. And that’s exactly what the stimulus did.