All known deposits of the mineral tanzanite are in Tanzania. Therefore, because Ashley collects only tanzanite stone...

Nicolette on August 25, 2014

question

Can you explain why choice C is incorrect?

4 Replies

Melody on August 29, 2014

We are told that every known deposit of the mineral tanzanite is in Tanzania. We also know that Ashley only collects tanzanite stones. Thus, she is unlikely to collect a stone that did not originate from Tanzania.

So, we are told that a specific stone comes only from one place. Ashley collects only that specific stone. Therefore, it is highly unlikely that a stone she collects was not originally from that one place.

Answer choice (C) states: "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."

The issue with answer choice (C) lies within the first and last sentences. We are told that frogs are the only animals known to live in the lagoon on Scrag Island. This means that no other animal lives in the lagoon. This, however, does not mean that frogs cannot also live in other places on the island. We only know that no other animal, but the frog, lives in the lagoon. The frogs of Scrag Island could be the lone residents of the lagoon, while also living in the jungle or by the river.

Answer choice (C) then concludes that since the owls of Scrag Island only eat frogs, they are unlikely ever to eat an animal that lives outside the lagoon. This, however, is not true. Along with living in the lagoon, the frog could also live by the river, meaning that the owls of Scrag Island could also eat animals that live by the river.

In contrast, we know from the stimulus that all known deposits of the mineral tanzanite are in Tanzania and that Ashley only collects tanzanite stones. Thus, it is true that Ashley is unlikely to collect a stone that was not originally from Tanzania.

Therefore, the reasoning in the stimulus is not similar to the reasoning in answer choice (C).

Hope that clears things up! Please let us know if you have any other questions.

Ashley on July 4, 2018

Is A wrong because it only talks about "many," or "some" frogs and there may be others that live outside the lagoon? Is D correct because it accounts for "each frog"?

Ashley on July 4, 2018

I meant E. Is D incorrect because it only talks about the frogs "yet discovered' and there might be other frogs unaccounted for?

Mehran on July 5, 2018

Hi @Ashley-Tien, thanks for your post.

It may be helpful first to ensure a full understanding of why (D) is the correct answer. Let's compare each part of the stimulus to each part of (D).

Stimulus: "All known deposits of the mineral tanzanite . . ."
Answer (D): "The only frogs yet discovered . . . "
Notice how both of these phrases tell you the same thing - that a particular thing (stone, frog) is known to come from only one place.

Stimulus: "Because Ashley collects only tanzanite stones . . ."
Answer (D): "The diet of all the owls on Scrag Island consists entirely of frogs . . ."
This narrows the universe - Ashley collects just one thing. The owls eat only frogs.

Stimulus: " . . . she is unlikely ever to collect a stone not originally from Tanzania"
Answer (D): " . . . the owls will probably never eat an animal that lives outside the lagoon."
These conclusions are supported by the premises which narrowed the universe of possibilities.

Answer (A) can be eliminated because you are not told that the frogs are restricted to one part of the island (the way that tanzanite is known to come from just one place).

Answer (E) can be eliminated because it is too extreme in the other direction, and speaks in absolutes. By contrast, the stimulus and correct answer choice (D) talk about what is "known" or "yet discovered" thus far, and conclude that certain outcomes are "unlikely" to occur or will "probably never" occur.

Hope this helps! Please let us know if you have any additional questions.