Logical reasoning PrepTest 109 · Section 4 · Question 5

Incorrect. The conclusion states that there are "moons" in S4, so this answer contradicts the conclusion.

Incorrect. This answer doesn't guarantee that the planet they orbit is planet Alpha, so it doesn't justify the conclusion.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Sufficient Premise

Stimulus Summary:
Moon → Orbits a planet in a solar system
Therefore - Moon in S4 → Orbits planet Alpha

Answer Anticipation:
When dealing with Strengthen with Sufficient Premise questions that use conditional logic, we want to track the connections that are made, and then find the gap in the argument.

One place to start is looking at the conclusion and identifying where there's overlap with the premises, and where there isn't. Here, the conclusion talks about specific moons and a specific planet, whereas the premises talk more generically.

With that in mind, we should consider what the premise does speak to that is in the conclusion. Looking there, we can see that the premise talks about all moons, so it applies to the ones discussed in the conclusion. However, it only talks about "some" planets, so it doesn't necessarily speak to planet Alpha.

What can we say about the moons in the conclusion based on that premise? That they must orbit a planet in a solar system. However, that doesn't guarantee that they orbit planet Alpha specifically. We need an answer that guarantees planet Alpha is the planet they're orbiting—likely by establishing that it's the only planet in the solar system.

Answer Explanation:
All moons orbit a planet, so all the moons in S4 orbit a planet. If Alpha is the only planet in that solar system, then the moons must all orbit it, and the conclusion is justified.

Key Takeaway:
For Strengthen with Sufficient Premise questions, starting by looking for overlap between the premises and conclusion (and seeing what concepts in the conclusion don't get mentioned in the premises) is usually a good place to start. This will let you know what about the conclusion can be proven, and what needs to be established for the argument to be valid.

Incorrect. This answer, if anything, suggests that the moons are split up between planets. It at least doesn't establish that Alpha is the only planet and thus the only one around which the moons are orbiting.

Incorrect. This answer doesn't establish that every moon orbits around Alpha, so it's a necessary premise more than a sufficient one.