Logical reasoning PrepTest 155 · Section 2 · Question 9

Incorrect. Rodents do, and rodent species are a minority. We don't know anything about other mammals, so we can't infer this answer.

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
First, there's some background on what a mammal is. Then, there are two "most" statements:
1) Most NA mammal species aren't rodents
2) Most NA mammals are rodents

Answer Anticipation:
Quantified statements ("most") generally are a point of focus in Must Be True questions where they show up. If an inference can be drawn by combining them in some way, it tends to be the answer.

Here, if most mammal species aren't rodents, but most mammals are rodents, then it must be the case that the rodent species tend to have more members than other mammalian species. In other words, if there are, say, only 3 rodent species, then there must be a lot of each of them.

Answer Explanation:
This answer combines the two most statements. If there are fewer rodent species than other mammals, but more individual rodents, each species of rodent has to have a lot of individuals.

Key Takeaway:
In Must Be True questions, quantified statements frequently lead to inferences, especially when there is more than one that can be combined!

Incorrect. The stimulus doesn't mention anything outside of North America, so this answer is out of scope.

Incorrect. This answer is tempting, but it's too specific. On average, there have to be more rodents per species than other mammals, but that doesn't mean that one non-rodent mammal can't be an outlier with a ton of members, brought down by the average number of other mammals below rodent levels.

Incorrect. Similar to (C), the stimulus doesn't mention anything outside of North America, so this answer is out of scope.