Logical reasoning PrepTest 130 · Section 1 · Question 24

Incorrect. Migration from where? The origin of the bears in the Preserve is key to whether the argument is valid or not. Without knowing if these bears migrated from other areas of the Valley, we can't tell if this answer choice weakens the argument.

Incorrect. This answer choice establishes that most of the increase in the Preserve's population came from outside the Valley, suggesting that the overall bear population has increased and strengthening the argument.

Incorrect. While this answer establishes that most of the increase in the Preserve's population came from other parts of the Valley, it also states that some of it came from outside the Valley. Since the conclusion only discusses an increase in the overall bear population, "some" increase due to outside migration is enough to support that conclusion, so this answer doesn't undermine the argument.

Incorrect. So close! However, this answer choice doesn't address the scale of the shift from the stimulus. While the bear population has decreased in other areas of the Valley, it has doubled in the Preserve. This answer would need to establish that the population in the other parts of the Valley decreased by a substantial enough number to account for that increase before we could conclude that the increase to the Preserve's population came at the expense of the Valley as a whole, thus undermining the conclusion that the bear population will increase.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
The Preserve is in the Valley. Most bears live in the Preserve. A road through the Preserve has been closed, and the Preserve's bear population has doubled. Therefore, keeping the road closed will cause the Valley's bear population to increase.

Answer Anticipation:
It's very easy to miss a key shift in this argument, making it much harder to find the correct answer. However, look at that conclusion carefully—what area is it about? Did you notice that it was about the Valley? It's easy to miss that the argument jumps from premises about the bear population in the Preserve to a conclusion about the bear population in the Valley.

Why is that a problem? After all, the Preserve is in the Valley, so won't the overall Valley population increase if the Preserve population increases? Only if the bear population increase in the Preserve comes from bears outside of the Valley. However, it's possible that the doubling of the Preserve's bear population over the past 8 years happened as bears from other parts of the Valley moved to the Preserve (maybe since there was less traffic with the road closed). The argument ignores this possibility, so the correct answer will likely highlight it.

Answer Explanation:
If the bear population of the Valley as a whole has stayed about the same despite the population in the Preserve (within the Valley) doubling, then it seems as if those bears likely migrated from other parts in the Valley. This answer calls into question an increase in the Preserve's bear population resulting in an overall increase in the Valley's bear population, thus undermining the argument.

Key Takeaway:
When the LSAT creates a distinction early on—especially when it distinguishes between two easily confusable elements, such as a Preserve and a Valley—be sure that you're tracking the two. This question is very difficult because it's easy to gloss over the shift in the conclusion when it hops to talking about the Valley after spending so much time in the premises discussing the Preserve.