Logical reasoning PrepTest 133 · Section 1 · Question 6

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
Heat resistance - Vacuum tubes beat semiconductors
Max current capacity - Semiconductors beat vacuum tubes
Heat resistance better AND Comparable in other significant respects → Better than semiconductor for digital circuits
not Comparable in other significant respects → not Better than semiconductor for digital circuits

Answer Anticipation:
This stimulus revolves around comparisons and a conditional rule, so we need to make heads and tails of it!

The comparisons are pretty straightforward—vacuum tubes beat semiconductors in one metric (heat resistance) but lose in another (max current capacity).

The conditional, on the other hand, is complex. It seems straightforward at first—if a component has better heat resistance, then it's better than semiconductors for digital circuits. Easy peasy. But then it takes a hard turn into difficult conditional land when it throws in that "but only if." That establishes a necessary condition, but we can't just tack it onto the conditional.

So what is that condition necessary for? It's necessary for something to be better than a semiconductor for digital circuits. That's how we got the second conditional—if something isn't comparable in other respects, then it's not better. However, we can also say that it adds a condition to the first conditional—that something that has better heat resistance AND is otherwise comparable is better than a semiconductor. While it's necessary for that to be true, it applies to the sufficient condition, as well.

With that noted, we can see that, based on the comparative statements, the vacuum tubes aren't comparable in other significant respects—they have a lower max current capacity—and so the second conditional lets us conclude that they aren't better than semiconductors for digital circuits. Let's find that answer.

Answer Explanation:
This answer reflects our anticipation. If components that aren't comparable to semiconductors in certain key respects—including max current capacity—aren't preferable for digital circuits, and vacuum tubes have a lower max current capacity, then we can conclude this answer.

Key Takeaway:
Complex conditional statements can be tricky to get right. Sometimes, it's more important to understand the statement than to have a perfect diagram. Here, noting that anything that wasn't comparable to semiconductors in key ways wasn't preferable to them in digital circuits was more important than getting both of the statements we diagrammed perfect.

Incorrect. First, the stimulus at best would establish at that point that vacuum tubes would be preferable for use in digital circuits, not that they would be used. Second, the stimulus only discusses maximum current capacity, not other significant respects, so there may be something else holding vacuum tubes back.

Incorrect. There's no indication that there isn't some other factor holding them back—price, size, or production capacity for instance.

Incorrect. Applications other than digital circuits are outside the scope of this argument.

Incorrect. Resistance to heat is the only advantage that the argument lists of vacuum tubes over semiconductors, but that doesn't mean it's the only one that exists.