Logical reasoning PrepTest 119 · Section 4 · Question 24

Incorrect. We can infer that the specimen has white flowers. However, we can't conclude that it has thorny seedpods—if you picked this answer, you illegally reversed conditional #3.

Incorrect. We can infer that the specimen has white flowers. However, we can't conclude that it lacks thorny seedpods—this would reverse and partially negate conditional #3.

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
(1) Fuzzy seeds → Long stems AND not White flowers
(2) Curled leaves → White flowers
(3) Thorny seedpods → Curled leaves
Specimen: Long stem AND Curled leaves

Answer Anticipation:
This question stem asks us to draw inferences about the specimen mentioned in the stimulus. Since the stimulus tells us two specific things about the specimen—it has a long stem and curled leaves—we should work through the conditionals with that information instead of trying to chain the conditional statements together.

Let's start with the long stem. Looking at the conditionals, that term shows up only in the first. However, a long stem is a necessary condition for having fuzzy seeds. Since it's not a sufficient condition, we can't draw any inferences from the long stem. Trying to take the contrapositive would talk about a plant without a long stem, so this first piece of information is a red herring—it's trying to get us to incorrectly conclude that the specimen has fuzzy seeds, but we're not falling for it.

The second thing we know about the specimen is that it has curled leaves. The second conditional allows us to infer that the specimen has white flowers. The third statement as curled leaves as a necessary condition, so we can't conclude anything from there.

If you stopped here, you'd be able to narrow down the answers, but you neglected to check for an important source of inferences—the white flowers. After we infer that the specimen has white flowers, we need to check to see if that allows for other inferences. Here, the first statement has a lack of white flowers as a necessary condition, so let's take the contrapositive there:
White flowers OR not Long stems → not Fuzzy seeds

OR sufficient conditions can be split up—either term by itself guarantees the necessary condition. Since this specimen does have white flowers, we can infer that it also doesn't have fuzzy seeds.

Let's find an answer that has some combination of white flowers and no fuzzy seeds.

Answer Explanation:
This answer matches our anticipation, so it's the correct answer. The fact that the specimen has curled leaves allows us to conclude that it was white flowers (conditional #2), and that inference that it has white flowers allows us to conclude that it lacks fuzzy seed (conditional #1).

Key Takeaway:
First, know how to work with complex conditionals, and when you can deal with the terms individually instead of collectively. Second, inferences sometimes lead to other inferences, so don't stop when you've made a one-step inference—see if there's a second step to make!

Incorrect. We can infer that the specimen lacks fuzzy seeds (conditional #2, and then conditional #1), so this answer is contradicted by the stimulus.

Incorrect. We can infer that specimen has white flowers (conditional #2), so this answer is contradicted by the stimulus.