Logical reasoning PrepTest 152 · Section 4 · Question 15

This argument jumps between belief and reality. That's a flaw, but it's not the same as the one in the given argument.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Flawed Parallel Reasoning

Stimulus Summary:
Children haven't gained much weight, on average, over the past 8 years, so the proportion of children who are obese can't have changed much, and therefore the childhood obesity epidemic is a myth.

Answer Anticipation:
Slow down there, Ray Kroc. The argument jumps between the average weight, to a determination about how that weight is spread between the population. If, over the past 8 years, half the children gained a lot of weight, and the other half got in great shape, the average might stay about the same while the proportion of those who are obese could have shot up.

Answer Explanation:
At this company, it's possible half the employees were fired and replaced with recent college grads earning next to nothing, while the other half gave themselves a nice raise. The average could be about the same, while the number of workers receiving a high salary drastically increased. This is the same error in reasoning.

Key Takeaway:
The LSAT likes to use averages to trick test takers, since most pre-law students get flustered by anything in the world of math. However, the concept it tests is almost always the same, so revisit a few of these questions to get it down!

This argument does have a flaw, in that the number of buildings overall could have drastically increased. That's different than the given argument's flaw, dealing with the difference between the average value of something and the distribution of it.

This argument deals with a spurious causal assumption, mainly that high-calorie dishes on menus drives weight gain. That's a much different assumption than the one in the given argument.

This is a tricky answer, but a good sign that it's incorrect is that the conclusion is about an average, not the premise. This argument's flaw is that it's only considering one possible change—an increase in housing costs—when there is another possibility it doesn't rule out—mainly, that household income has gone down.