LSAT Explanation PT 45, S1, Q11: The average cost of groceries will

LSAT Question Stem

The flawed reasoning in the argument above most closely parallels the reasoning in which one of the following? 

Logical Reasoning Question Type

This is a Parallel Flaw question. 

Correct Answer

The correct answer to this question is C. 

LSAT Question Complete Explanation

First, let's analyze and summarize the argument in the passage. The argument states that since the average cost of groceries will rise next month, we can expect butter and eggs to cost more next month. This argument has a premise (the average cost of groceries will rise) and a conclusion (butter and eggs will cost more). The reasoning in this argument is flawed because it assumes that if the average cost of groceries rises, every individual item, such as butter and eggs, will also rise in price. This is an error of division, where a characteristic of the whole (groceries) is incorrectly applied to its parts (butter and eggs).

An "Evaluate" question for this argument could be: "Will the price increase in groceries affect all individual items, including butter and eggs, or only some items?"

Now let's examine the answer choices, keeping in mind that we are looking for an answer that contains a similar flaw to the one in the passage.

a) This answer choice is incorrect because it projects a past trend into the future, whereas the argument in the passage involves the future but not the past. Additionally, this choice does not use a general average and apply it to specific items. Instead, a single item (gasoline) is addressed throughout the answer.

b) This choice states that only two outcomes are possible and concludes that since one of the options is unlikely to occur, the other option must occur. Although the reasoning is flawed, it is not analogous to the flawed reasoning found in the passage.

c) This is the correct answer choice. The answer addresses a characteristic (amount of time spent watching television) of a general group (people younger than 20) and indicates that the average characteristic is increasing. The answer then concludes that the characteristic of a part (fourth graders) of the general group must also have risen. Similar to the argument in the passage, this argument ignores the fact that an average increase does not mean that every part of the group has increased.

d) This choice contains valid conditional reasoning and does not contain the same flawed use of an average and its component parts as the argument in the passage. Therefore, it is not the correct answer choice.

e) This choice also contains conditional reasoning and does not have a part-to-whole relationship within the answer. Therefore, it is incorrect on that count as well.

In conclusion, the correct answer choice is (c), as it most closely parallels the flawed reasoning found in the passage, committing the same error of division.