LSAT 141 | Section 4 | Logical Reasoning: Q18

LR Question 18 Explanation

QUESTION TEXT: So far this summer there has been no rain in the…

QUESTION TYPE: Flawed Parallel Reasoning

CONCLUSION: It will probably rain before the end of summer.

REASONING: It usually rains a few inches in the valley each summer. This summer there’s been no rain, and there’s only one week of summer left.

ANALYSIS: This is a bad argument. The author ignores the possibility that this summer is unusual and there’s a drought.

Abstractly, the error is: assuming that something will happen just because it hasn’t happened yet.

Statistics don’t work like that. You aren’t “due” to have rain, success, failure, etc. The fact that something hasn’t happened in a while decreases the odds that it will happen, unless you know it must happen for certain.

___________

1. This is a good argument. It just says there “may” be errors. It’s certainly possible errors exist.
   To be right, this answer should have said there “probably” will be errors.
2. This is a good argument. Errors are unlikely even in a whole issue. So errors are even less likely in a few pages of an issue.
3. CORRECT. This takes evidence from what’s true on average and assumes it must always happen. But the lack of errors so far makes it less likely there are errors in the final pages.
   “A few errors on average” could mean that many issues have no errors, and some issues have many errors. Averages aren’t evenly distributed.
4. This is a good argument. If there are rarely errors in an entire issue, then it’s even less likely there will be errors in a few pages of an issue.
5. It’s hard to say if this argument is good or bad. We’d need to know more about Aisha’s proofreading skills to be sure. Either way, this argument isn’t obviously bad like the stimulus. If there are usually errors, then it is odd that Aisha found none in the entire issue.
   The correct answer is different in that it talks about finding errors in a few pages. That’s far less likely.