Logical reasoning PrepTest 109 · Section 1 · Question 23

Incorrect. The second premise here is an OR statement, so we can eliminate it since the stimulus doesn't feature a parallel element.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Valid

Question Type:
Parallel Reasoning

Stimulus Summary:
not Fly to Chengdu → not Fly to Lhasa
Fly to Chengdu → Fly to Xian
Therefore — Fly to Lhasa → Fly to Xian

Answer Anticipation:
This argument presents three conditional statements (indicator words, in order: without" "must" "cannot avoid"). We treated "without" as "if not," but if you had used another method, you would have ended up with the contrapositive of that first statement. That would have made it easier to see that this argument is valid! Take the contrapositive of that first statement to see how the argument chains together!

So we're looking for an argument that goes:
A → B
B → C
Therefore — A → C

That said, there's one other element that we should look out for—the stimulus does have a timeline element to it, and we know that timeline elements are relevant to the logic of an argument and frequently tested on the exam. The traveler here would have to go to Xian first, then Chengdu, and then finally Lhasa. In short, the order of the flights goes in the opposite direction of the conditionals. Let's be sure to check any answer we think is correct for that element, as well, before filling in that bubble.

Answer Explanation:
This argument has the timeline element and two conditionals that appear to chain together, so we should dive in:
not Green level → not Yellow level
not White level → not Green level
Therefore — Yellow level → White level

If you take the contrapositive of the premises to match up with the conclusion, you can see that this follows the same structure. Additionally, the white level happens first, followed by green, and then yellow—the timeline moves in the opposite direction of the conditional. This answer is therefore correct.

Key Takeaway:
If you identify the relevant elements in the stimulus, you can eliminate answers that don't match up with them. That means eliminating answers that are missing a key element or have an element that you know didn't appear in the stimulus.

Incorrect. This argument's second premise isn't a conditional. It says a microscope can be used to examine spores, but that "can" means the statement is less than certain and thus not conditional.

Incorrect. The second premise here is an OR statement, and the stimulus doesn't have a matching OR premise, so this answer can be eliminated.

Incorrect. The second premise and the conclusion in this answer are some statements, so this argument isn't parallel to the stimulus where each statement is a conditional.