Logical reasoning PrepTest 120 · Section 3 · Question 1

Incorrect. While something about the manufacturing of fiber-optic cable is more expensive than copper cable, it's not necessarily the base materials. It could be that the base materials for fiber-optic cables are a bit cheaper than copper, but the method of turning those materials into cable is much more expensive.

Incorrect. There's no indication that copper cable-based networks are reaching their limits, so this answer is out of scope.

Incorrect. The number of signals that can be transmitted aren't mentioned in the stimulus, so this answer is out of scope.

Incorrect. The speed of transmission isn't mentioned and is thus out of scope.

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
Fiber-optic vs. Copper telephone cable:
(1) FO cable is more expensive
(2) FO network is less expensive because copper needs more frequent amplification

Answer Anticipation:
The stimulus here compares a fiber-optic network with a copper one. The cable for the former is more expensive, but the latter is more expensive overall because it needs more frequent amplification. Since the stimulus notes that the reason the latter is more expensive is this amplification, it must be the case that the cost of amplification more than makes up for the lower cost of the cable. Let's find an answer stating that!

Answer Explanation:
Copper cable-based networks have cheaper cable costs. Fiber-optic cable-based networks are cheaper overall because they have to amplify signals less. Therefore, it must be the case that the cost of amplification overcomes the savings in the cable, as this answer choice states.

Key Takeaway:
First, pay attention to comparisons! They allow for inferences, and the LSAT frequently uses them to lead to a correct answer in a Must Be True question. Second, pay attention when the stimulus of a Must Be True question explains the reason behind something (ÒThis is becauseÓ), as this strongly connects the explanation to the phenomenon (almost always in a causal manner).