LSAT 157 | Section 2 | Logical Reasoning: Q7

LR Question 7 Explanation

QUESTION TEXT: The mu mesons generated by cosmic rays just outside …

QUESTION TYPE: Complete the Argument

CONCLUSION: Mu mesons moving near the speed of light decay faster than mu mesons nearly at rest.

REASONING:

1. Mu mesons generated by cosmic rays outside Earth’s atmosphere (hereafter “cosmic mu mesons”) travel at nearly the speed of light.
2. Mu mesons generated in the lab (“lab mu mesons”) are almost at rest.
3. It takes much more time for a cosmic mu meson to reach the detectors on Earth than it takes for a lab mu meson to decay.
4. If cosmic mu mesons decayed at the same speed as lab mu mesons, we would detect 1% of the amount we actually detect.

ANALYSIS: Hoo boy, there’s a lot of unfamiliar science words. The LSAT wants you to panic and you should not. You don’t need to know what a mu meson is, you don’t need to know what cosmic rays are, and you don’t need to know the speed of light. You just need to parse the question and identify the point – some mu mesons travel faster than others, and the data is inconsistent with the idea that both types decay at the same rate.

Once you’ve identified the reasoning, as above, this question is easy. Remember that the LSAT will never expect you to have this kind of intense science knowledge. If it doesn’t explain what a mu meson is, it’s probably not necessary for the answer!

Here, the conclusion will be the reason we are detecting more cosmic mu mesons than we would expect. It’s probably related to their speed, because that’s a difference between the two types that was specifically noted in the stimulus.

___________

1. If they took longer to reach Earth than we thought, more should be decaying before reaching the detector. But they aren’t – it’s the opposite!
2. This is wrong for a similar reason as A. We are detecting more cosmic mu mesons than we would expect, but these answers give conclusions that would follow if we weren’t detecting enough.
3. This answer, again, gives an opposite conclusion. See B.
4. CORRECT. If mu mesons traveling fast (cosmic mu mesons) decay more slowly than those nearly at rest (lab mu mesons), then more will be detected than we would expect if we assumed they decay at the same speed!
5. This is not the correct conclusion. It directly contradicts part of the stimulus, which tells us that mu mesons generated by cosmic rays travel at nearly the speed of light.

Recap: The question begins with “The mu mesons generated by cosmic rays just outside “. It is a Complete the Argument question. Learn how to master LSAT Complete the Argument questions on the LSAT Logical Reasoning question types page.