LSAT Explanation PT 41, S3, Q20: On some hot days the smog

LSAT Question Stem

The reasoning in the argument is flawed in that the argument 

Logical Reasoning Question Type

This is a Flaw question. 

Correct Answer

The correct answer to this question is B. 

LSAT Question Complete Explanation

Let's first break down and analyze the argument in the passage. The passage is structured as follows:

Premise 1: On some hot days (HD), the smog in Hillview reaches unsafe levels (SUL).

Premise 2: On some hot days (HD), the wind blows into Hillview from the east (WBE).

Conclusion: On some days when the wind blows into Hillview from the east (WBE), the smog in Hillview reaches unsafe levels (SUL).

To make this more understandable, let's use a simple example. Imagine we have a bag of 10 marbles. On some days (say 3), the marbles are red (SUL), and on some days (say 3), the marbles are shiny (WBE). The argument is concluding that on some days, the marbles are both red and shiny. However, we don't have enough information to determine if this is true or not.

An "Evaluate" question for this argument could be, "On the days when the wind blows into Hillview from the east, does the smog in Hillview reach unsafe levels?"

Now, let's discuss each answer choice:

a) This answer choice is incorrect because the argument doesn't mistake a condition that sometimes accompanies unsafe levels of smog for a condition that necessarily accompanies unsafe levels of smog. The argument is flawed because it assumes that just because both events happen on some hot days, they must happen together on some days.

b) This is the correct answer choice. The argument fails to recognize that one set (HD) might have some members in common with each of two others (SUL and WBE) even though those two other sets (SUL and WBE) have no members in common with each other. In our marble example, this means that just because there are some red marbles and some shiny marbles, it doesn't necessarily mean that there are marbles that are both red and shiny.

c) This answer choice is incorrect because the argument uses the term "unsafe" consistently in both the premise and the conclusion.

d) This answer choice is incorrect because each premise is plausible regardless of the truth of the conclusion. The argument doesn't rely on the conclusion being true for the premises to be plausible.

e) This answer choice is incorrect because the argument does not involve causal reasoning. The conclusion states that the two events (SUL and WBE) happen together, but it doesn't try to establish a cause-and-effect relationship between them.