Logical reasoning PrepTest 123 · Section 3 · Question 8

Flawed

Errors in Reasoning Questions

99% of people in a sample of over 100 preferred a Fabric-Soft towel to a towel washed without Fabric-Soft, so Fabric-Soft is the most effective fabric softener.

Whenever a study is done, a sampling error should be considered. Here, while it might seem small, over 100 people will generally be a large enough sample to justify a conclusion unless we're given a specific reason to doubt the representativeness of that sample. There's nothing in the stimulus suggesting the people in the study aren't representative of people generally, but a correct answer could bring up a reason to believe that, so we should be thinking about that as we analyze them.

Separate from a potential sampling error, there's a huge term shift here. If you're not seeing a flaw, a good place to look is the conclusion to see if there are any concepts that are new, and are thus not supported by the premises. Here, the conclusion is that Fabric-Soft is the most effective fabric softener—in other words, it's more effective than any other softener. There are two new ideas there. First, effectiveness. The study is about consumer preference, which isn't the same as effectiveness. Second, the study compared a Fabric-Soft towel to a towel washed without fabric softener. To support the conclusion, the study would have to compare Fabric-Soft to all other fabric softeners.

To sum up, we have three potential answers:

(1) An answer pointing out a reason to believe the sample is unrepresentative, though this is less likely since no information in the stimulus suggests this.

(2) An answer highlighting the jump from consumer preference to effectiveness.

(3) An answer highlighting the jump from a comparison with a softener-less towel to a conclusion with a comparison to all other fabric softeners.