PrepTest 157

[lcid:3725] Prep Test 157 LSAT — Logical Reasoning — S2 Logical reasoning

Question prompt

The mu mesons generated Remaining source text redacted.
Why the credited answer is right

Credited answer: D

The notes below walk through why it fits the stem and how to eliminate the rest.

Argument or Facts

Argument

Strategy Overview

Argument or facts for both speakers? Always argument Completing with a premise or conclusion? Check for the word preceding the blank space to see. "Because," "since," "for," "as," etc. = completing with a premise. Complete with a premise? Treat as a Strengthen question "Therefore," "thus," "hence," "so," etc. = completing with a conclusion Complete with a conclusion? Treat as a Must Be True question

Answer Anticipation

This Argument Completion question asks us to add the argument's conclusion. We know this because the author uses the tonal word "Apparently," and such tonal words are often used to introduce the conclusion. Since we're completing this argument with a conclusion, we can treat it as a Must Be True question — the other, more common question type in which we take a set of facts and derive a valid conclusion. So, what must be true based on these facts? We get a lot of facts about mu mesons — whatever those are — but the only facts we need to draw this conclusion come from the "if-then" statement in the penultimate sentence. That tells us that if mu mesons traveling at the speed of light decayed as fast as lab mu mesons, we'd detect far fewer mu mesons than we do. We can diagram that and take its flipside: P: Mu Mesons Decayed Like Lab Mu Mesons → Detect Fewer Mu Mesons / NOT Detect Fewer Mu Mesons → NOT Mu Mesons Decayed Like Lab Mu Mesons The "then" condition also subtly asserts a factual premise. Notice how it says we'd detect far fewer mu mesons than "we actually do detect." So, we know we don't detect fewer mu mesons. Let's add that to our premise list: P: Mu Mesons Decayed Like Lab Mu Mesons → Detect Fewer Mu Mesons / NOT Detect Fewer Mu Mesons → NOT Mu Mesons Decay Like Lab Mu Mesons P: NOT Detect Fewer Mu Mesons We can apply the factual premise to our flipside. The flipside tells us that if we do not detect fewer mu mesons, then mu mesons traveling at the speed of light do not decay as quickly as mu mesons in a lab. So, we can conclude that mu mesons traveling at the speed of light do not decay as quickly as mu mesons in a lab. P: Mu Mesons Decayed Like Lab Mu Mesons → Detect Fewer Mu Mesons / NOT Detect Fewer Mu Mesons → NOT Mu Mesons Decay Like Lab Mu Mesons P: NOT Detect Fewer Mu Mesons

Answer choices

  1. A
    take longer to reach Remaining source text redacted.
    Why choice A is not credited

    We know that the correct answer should say that mu mesons traveling at the speed of light do not decay as quickly as mu mesons in a lab. This answer choice doesn't say that, so it can be a quick elimination.

    Even if we didn't make that anticipation, we could conclude that this isn't an appropriate way to complete the argument. Other than telling us that mu mesons travel at nearly the speed of light, the passage doesn't provide any information on how long it takes them to reach Earth. And just because mu mesons in a laboratory are stationary does not mean that mu mesons that travel to Earth are slower than we once thought.

  2. B
    are quite difficult to Remaining source text redacted.
    Why choice B is not credited

    We know that the correct answer should say that mu mesons traveling at the speed of light do not decay as quickly as mu mesons in a lab. This answer choice doesn't say that, so we can cross it off without a second thought.

    Even if we didn't make that anticipation, we could conclude that this isn't an appropriate way to complete the argument. The passage doesn't suggest that mu mesons are difficult to detect with our current equipment. The penultimate sentence says that we do detect quite a few mu mesons — 100 times more than we would if they decayed as quickly as lab mu mesons, anyway — so we don't have any reason to think our equipment makes it difficult to detect mu mesons.

  3. C
    are much less numerous Remaining source text redacted.
    Why choice C is not credited

    We know that the correct answer should say that mu mesons traveling at the speed of light do not decay as quickly as mu mesons in a lab. This answer choice doesn't say that, so we can eliminate it unhesitatingly.

    Even if we didn't make that anticipation, we could conclude that this isn't an appropriate way to complete the argument. The penultimate sentence says that we do detect quite a few mu mesons — 100 times more than we would if they decayed as quickly as lab mu mesons. And we don't know whether we previously thought we'd detect even more mu mesons — the passage doesn't say anything about those past beliefs.

  4. D
    decay more slowly than Remaining source text redacted.
    Why choice D matches the stem

    We know that the correct answer should say that mu mesons traveling at the speed of light do not decay as quickly as mu mesons in a lab. This answer choice says that mu mesons traveling at the speed of light decay more slowly than mu mesons almost at rest. This isn't exactly what we anticipated, but it's equally supported. The passage says that mu mesons in a laboratory are "nearly at rest." Since this answer choice matches our anticipation, we can select it and advance to the following question.

  5. E
    are probably not generated Remaining source text redacted.
    Why choice E is not credited

    We know that the correct answer should say that mu mesons traveling at the speed of light do not decay as quickly as mu mesons in a lab. This answer choice doesn't say that, so we can immediately toss it away.

    Even if we didn't make that anticipation, we could conclude that this isn't an appropriate way to complete the argument. The passage gives us no reason to suppose that cosmic rays don't generate mu mesons. In fact, we're told that the mu mesons that are generated by cosmic rays travel nearly at the speed of light, and the beginning of the conclusion specifies that we're talking about those mu mesons! So, adding (E) to the blank space would make a self-contradictory statement.

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