Logical reasoning PrepTest 144 · Section 4 · Question 13

Incorrect. There's no shift in the meaning of average here—it's not even clear what that second meaning would be.

Incorrect. The stimulus's conclusion is about the Andersen families real income, and their income today is compared to the real income average, so it does take inflation into account.

Incorrect. It doesn't overlook that possibility—it talks averages and then talks about a specific example, so the incomes of most families are already incorporated into that average.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Avg. family income has increased over the past 5 years, and the Andersen family's income is average, so it must have gone up over the past 5 years.

Answer Anticipation:
This argument establishes a timeline and comparisons. The timeline is when a certain change happened, and the comparisons are between: 1) avg. family income from 5 years ago and today, and 2) the Andersen family's income today and the avg. family income today. The conclusion then compares the Andersen family's income today to that of 5 years ago.

However, there's one part of that timeline/comparison that's missing—the Andersen family's income from 5 years ago! The argument concludes that it went up, but there's no indication that their income was at the average from 5 years ago. It's possible their income was above the average 5 years ago and it hasn't changed, thus letting the average "catch up."

The correct answer, therefore, will have to address this lack of setting a baseline of the Andersen family's income from 5 years ago.

Answer Explanation:
This answer highlights that it never establishes a baseline against which to compare the Andersen family's income against where it used to be. If the Andersen family's real income was above average in the recent past, then the conclusion doesn't hold.

Key Takeaway:
Whenever the LSAT notes a timeline, pay attention. Whenever the LSAT makes a comparison, pay attention. When the LSAT creates a timeline to compare things over time, really pay attention!

Incorrect. If there's no reason to doubt the data, then it's not an assumption to rely on that data on the LSAT. Even then, the argument doesn't rely on there being no errors, just that the errors either aren't big enough to alter the conclusions or that they're random enough to cancel out.