Logical reasoning PrepTest 116 · Section 3 · Question 9

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
(1) Lecturer AND Effective teacher → Eccentric
(2) Lecturer AND not Eccentric → Effective teacher
(3) Effective teacher → Good communicator

Answer Anticipation:
This is a tricky Must Be True stimulus because there are several terms that show up as both sufficient and necessary conditions, and as part of complex conditions (those AND sufficient conditions).

While there are several inferences that can be made here based on how terms overlap with each other, the only clear chain we can build is between statements 2 and 3:
Lecturer AND not Eccentric → Effective teacher → Good communicator

So that's one potential answer. However, there are other ways these statements interact, so we should be flexible in analyzing answer choices. Let's give ourselves as much time as possible to do so by getting to the answers quickly.

Answer Explanation:
To reach this answer, we'd need to make an inference using the first and third statements. And while the sufficient conditions aren't exactly the same, we can make this inference! The stimulus establishes that each of these groups exist, so there are some lecturers who are effective teachers. Those individuals are both eccentric and good communicators. Therefore, there are some good communicators who are eccentric—the lecturers who are effective teachers.

Key Takeaway:
There are inferences that can be drawn from conditionals that don't use the straightforward conditional rules (transitive property/chaining; quantifier combos). While rare, these do show up in questions, so work through answers by identifying which statements would need to be combined to lead to the answer and then see if those statements can serve as a basis for that inference.

Incorrect. This answer is a reversal of the third conditional, so it's not supported by the stimulus.

Incorrect. We don't know anything about lecturers who are not effective teachers, so this answer is out of scope (an illegal negation).

Incorrect. For this, we'd need to know that most lecturers who are good communicators are effective teachers, but there's no statement that allows for that inference.

Incorrect. This answer cannot be true. A non—eccentric lecturer is an effective teacher, but all effective teachers are good communicators, so none of them can fail to be good communicators.