Logical reasoning PrepTest 124 · Section 1 · Question 7

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
(1) not Substance that superconducts above -148C → not Economically feasible superconductor
(2) Substance that superconducts above -148C → Alloy of N and G
(3) Alloy of N and G - not Substance that superconducts above -160C

Answer Anticipation:
There's a lot of science and Celsius thrown our way in this question, but let's forget that and focus on what we can understand—the conditional logic! From that first indicator word ("unless"), we should start thinking about using diagrams to understand this stimulus, and that's reinforced by the second sentence being conditional, as well.

First, we diagrammed that opening "unless" as "if not"—if you used a different method and ended up at the contrapositive, no worries at all! That's still correct. The second sentence is a more straightforward if statement, and the last statement tells us something that's true of all of a certain type of alloy, so we can diagram that, as well.

The first thing to notice is that the first two statements share a sufficient condition term, albeit in opposite negation states, so we need to take the contrapositive of one of them. Let's do the first one to get rid of those negations and combine them:
Economically feasible superconductor → Substance that superconducts above -148C → Alloy of N and G

That last statement, however, tells us that an alloy of N and G won't superconductor above -160C, which means that it certainly won't conduct above -148C (remember, a "higher" negative number is a "lower" number, just like someone who has -$160 has less money than someone who has -$148). So let's take the contrapositive:
not Alloy of N and G → not Substance that superconducts above -148C → not Economically feasible superconductor

Since an alloy of N and G can't superconductor above -148C, the conditional chain guarantees us that there isn't an economically feasible superconductor, and that's what we should look for in the answer choices.

Answer Explanation:
This answer reflects our anticipation. If only an alloy of N and G could make an economically feasible superconductor, but such an alloy doesn't meet the requirements to do so, then the dream of such a product isn't meant to be.

Key Takeaway:
Don't get bogged down in the science of a passage. When such a passage relies so heavily on science, it's mostly there to obscure and hide a type of logic that we're more familiar with. Find that underlying logic and you should be good to go!

Incorrect. This answer directly contradicts the second conditional statement—any substance that superconducts over -148C is an alloy of N and G.

Incorrect. This answer is a negation of the initial conditional statement.

Incorrect. The argument implies that they do, just not economically.

Incorrect. While they can't be economically used in superconductors, they might find economical uses in other applications.