Logical reasoning PrepTest 151 · Section 4 · Question 15

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Car manufacturers claim fuel economy that I have never been able to get in my three cars. Therefore, these claims are inflated.

Answer Anticipation:
The Columnist tells us exactly how large her sample size is—3. That's not nearly large enough to draw a conclusion about a single car manufacturer even if all 3 of those cars were all made by the same company, let alone to draw a conclusion about all car manufacturers. This is a rare example of an argument with a sampling flaw of having too small a sample.

There's also another issue here—the claim is about fuel economy under "normal driving conditions," but the Columnist never states that she drives under such conditions (maybe she lives on top of a snow-covered mountain with lots of twists and turns in the roads). However, in stating that her experience fuel economy is not "even close" to the stated fuel economy, she's built in some wiggle room to account for different driving conditions, so this is less likely to lead to a correct answer.

Answer Explanation:
A sample of 3 is not a large enough sample to draw a conclusion about essentially anything, so this answer is correct.

Key Takeaway:
Single-digit samples, when specifically noted, are not big enough to justify a conclusion.

Incorrect. There is a bit of a shift between the claims of the manufacturers and the columnist. Their claims are based on "normal" driving conditions, and the columnist doesn't discuss driving conditions by her. However, at most, the columnist assumes that the driving conditions she experienced were normal, not that all regions have those normal conditions. (And she doesn't even really assume she had normal driving conditions, as she states that the fuel economy she got wasn't even close to those claimed, suggesting that driving conditions probably couldn't themselves account for the discrepancy).

Incorrect. The Columnist concludes that the claim was unreliable ("inflate[d]"), so she doesn't overlook this possibility.

Incorrect. While the Columnist believes their claims of fuel economy are inflated, she doesn't suggest that the actual fuel economy is under the minimum standards.

Incorrect. While the Columnist may fail to address whether her situation matches the conditions under which the manufacturers' claims are said to apply ("normal driving conditions"), that's not the same as using the term "fuel economy" to mean two different things. In both cases, it means something about how far someone can drive on a given amount of fuel—the question is just whether the context in which that is measured is the same.