LSAT 104 – Section 1 – Question 23

LSAT 104 - Section 1 - Question 23

December 1998

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Question
QuickView		 Type Tags Answer
Choices		 Curve Question
Difficulty		 Psg/Game/S
Difficulty		 Explanation
PT104 S1 Q23
+LR
Flaw or descriptive weakening +Flaw
Math +Math
A
10%
165
B
6%
164
C
52%
172
D
24%
165
E
8%
163
160
168
176
 +Hardest 149.106 +SubsectionMedium

J.Y.’s explanation

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Research indicates that 90 percent of extreme insomniacs consume large amounts of coffee. Since Tom drinks a lot of coffee, it is quite likely that he is an extreme insomniac.

Summarize Argument
The author concludes that it’s likely Tom is an extreme insomniac. This is based on the fact that 90 percent of extreme insomniacs drink lots of coffee, and Tom drinks lots of coffee.

Identify and Describe Flaw
The author misinterprets the claim “Most A are B” as “Most B are A.” Although 90 percent of extreme insomniacs drink lots of coffee, that doesn’t tell us anything about what proportion of lots-of-coffee drinkers are extreme insomniacs. It could be that the vast majority of lots-of-coffee drinkers aren’t extreme insomniacs, even if most extreme insomniacs drink lots of coffee.

A
It fails to acknowledge the possibility that Tom is among the 10 percent of people who drink large amounts of coffee who are not extreme insomniacs.
The premises don’t establish that only 10 percent of people who drink lots of coffee are not extreme insomniacs. Also, the conclusion doesn’t say that Tom definitely is an extreme insomniac. So, the author acknowledges that he might not be an extreme insomniac.
B
It fails to consider the possible contribution to extreme insomnia of other causes of insomnia besides coffee.
The author’s argument does not make any assumptions about cause. The issue is whether membership in the set of people who drink lots of coffee implies a likelihood of membership in the set of people who are extreme insomniacs.
C
It relies on evidence that does not indicate the frequency of extreme insomnia among people who drink large amounts of coffee.
The author relies on the fact that 90% of extreme insomniacs drink lots of coffee. This does not reveal the frequency (i.e. proportion) of extreme insomnia among people who drink lots of coffee. It could be that only a small % of lots-of-coffee drinkers have extreme insomnia.
D
It draws an inference about one specific individual from evidence that describes only the characteristics of a class of individuals.
The author does not commit the whole-to-part fallacy. The issue is misinterpretation of the claim “90% of extreme insomniacs consume lots of coffee.” This statistic is not a claim about a class — it’s a claim about 90% of the individuals within the class.
E
It presumes without warrant that drinking coffee always causes insomnia.
The author doesn’t make any assumptions about cause. The issue is whether membership in the set of people who drink lots of coffee implies a likelihood of membership in the set of people who are extreme insomniacs.

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LSAT PrepTest 104 Explanations

Section 1 - Logical Reasoning

Section 2 - Reading Comprehension

Section 3 - Reading Comprehension

Section 4 - Logical Reasoning

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