LSAT 131 – Section 2 – Question 20

LSAT 131 - Section 2 - Question 20

December 2009

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Question
QuickView		 Type Tags Answer
Choices		 Curve Question
Difficulty		 Psg/Game/S
Difficulty		 Explanation
PT131 S2 Q20
+LR
Flaw or descriptive weakening +Flaw
Sampling +Smpl
A
10%
162
B
18%
163
C
11%
159
D
57%
166
E
5%
158
147
161
174
 +Hardest 147.936 +SubsectionMedium

Quality control investigator: Upon testing samples of products from our supplier that were sent by our field inspectors from various manufacturing locations, our laboratory discovered that over 20 percent of the samples were defective. Since our supplier is contractually required to limit the rate of defects among items it manufactures for us to below 5 percent, it has violated its contract with us.

Summarize Argument
The author concludes that the supplier’s rate of defects for items it manufactures is not below 5 percent, as the contract requires. This is based on the fact that after testing samples of products sent by field inspectors from various manufacturing locations, the lab found that over 20% of the samples were defective.

Identify and Describe Flaw
The author assumes that the rate of defect in the samples sent by field inspectors is representative of the rate of defect in the overall set of products manufactured by the supplier. This overlooks the possibility that the samples selected have a higher rate of defect than the average product (perhaps because the field inspectors might be looking for potentially defective items).

A
bases its conclusion on too small a sample of items tested by the laboratory
We have no reason to think the sample of items sent by the inspectors is too small. In order to pick (A), we need some textual hook in the stimulus to suggest the sample size is too small.
B
presumes, without providing justification, that the field inspectors were just as likely to choose a defective item for testing as they were to choose a nondefective item
The assumption is that rate of choosing defects did not exceed the actual defect rate. (Ex. Actual rate is 25% defects, and inspectors chose defective items 25% of the time, nondefect 75%.) This doesn’t require chance of choosing defect to be equal to choosing nondefect (50-50).
C
overlooks the possibility that a few of the manufacturing sites are responsible for most of the defective items
This doesn’t undermine the argument, because we have no reason to think that a few sites being responsible for most defects would skew the defect rate in the inspectors’ sample. We have no reason to think the inspectors disproportionately picked items from these few sites.
D
overlooks the possibility that the field inspectors tend to choose items for testing that they suspect are defective
This undermines the argument, because it shows that the sample selected by inspectors might have a higher rate of defect than the average product produced by the supplier. This is why we can’t assume the over 20% defect rate in the sample applies to the overall set of products.
E
presumes, without providing justification, that the field inspectors made an equal number of visits to each of the various manufacturing sites of the supplier
The author does assume that the manner in which the inspectors collected items for the sample was not biased in a way that made the defect rate in the sample unrepresentative of the overall defect rate, but this doesn’t require any view about the number of visits.

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LSAT PrepTest 131 Explanations

Section 1 - Logical Reasoning

Section 2 - Logical Reasoning

Section 3 - Logical Reasoning

Section 4 - Reading Comprehension

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