LSAT Explanation PT 37, S2, Q26: All known deposits of the mineral

LSAT Question Stem

Which one of the following is most similar in its reasoning to the argument above? 

Logical Reasoning Question Type

This is a Parallel question. 

Correct Answer

The correct answer to this question is D. 

LSAT Question Complete Explanation

This is a Parallel Reasoning question, which means we need to find the answer choice that has a similar structure and reasoning to the argument in the passage.

The passage's argument can be summarized as follows:

Premise: Tanzanite stones are found only in Tanzania (T -> Tz)

Premise: Ashley collects only Tanzanite stones (A -> T)

Conclusion: Ashley is unlikely to collect stones not originally from Tanzania (A -> Tz)

Now let's analyze each answer choice:

a) The lagoon on Scrag Island is home to many frogs. Since the owls on Scrag Island eat nothing but frogs from the island, the owls will probably never eat many frogs that live outside the lagoon.

This answer choice doesn't have the same structure as the passage. The first premise should be "All A's are B" (all Tanzanite stones are in Tanzania), not "Many A's are B" (the lagoon on Scrag Island is home to many frogs). Therefore, this answer choice is incorrect.

b) Every frog ever seen on Scrag Island lives in the lagoon. The frogs on the island are eaten only by the owls on the island, and hence the owls may never eat an animal that lives outside the lagoon.

The conclusion in this answer choice is not parallel to the passage's conclusion. Furthermore, it does not suggest that the owls on the island eat only Scrag Island frogs. It is possible that the owls may eat other animals as well. This answer choice is incorrect.

c) Frogs are the only animals known to live in the lagoon on Scrag Island. The diet of the owls on Scrag Island consists of nothing but frogs from the island. Therefore, the owls are unlikely ever to eat an animal that lives outside the lagoon.

This answer choice seems attractive at first glance, as the second premise and conclusion match the passage. However, the first premise is not parallel to the passage. If frogs are the only animals known to live in the lagoon, it doesn't mean they don't live elsewhere on the island. This answer choice is incorrect.

d) The only frogs yet discovered on Scrag Island live in the lagoon. The diet of all the owls on Scrag Island consists entirely of frogs on the island, so the owls will probably never eat an animal that lives outside the lagoon.

This answer choice has the correct structure and reasoning:

Premise (1): Island frogs live only in the lagoon (F -> L)

Premise (2): Owl diet consists of only Island frogs (O -> F)

Conclusion: Owls are unlikely to eat animals that live outside the lagoon (O -> L)

This answer choice is correct.

e) Each frog on Scrag Island lives in the lagoon. No owl on Scrag Island is known to eat anything but frogs on the island. It follows that no owl on Scrag Island will eat anything that lives outside the lagoon.

The conclusion in this answer choice is too certain compared to the passage's conclusion, which is about the probability that Ashley is unlikely to collect a stone not originally from Tanzania. This answer choice is incorrect.

Therefore, the correct answer is (d).