LSAT 118 | Section 1 | Logical Reasoning: Q11

LR Question 11 Explanation

QUESTION TEXT: The average cost of groceries will rise again next month …

QUESTION TYPE: Flawed Parallel Reasoning

CONCLUSION: Butter and eggs will cost more next month.

REASONING: The average cost of groceries will go up next month.

ANALYSIS: This is a classic whole-to-part flaw. It’s one of the flaws you should train yourselves to recognize.

Imagine I say that the average height in the United States will go up next year. Does that mean that Samuel from Nebraska and Joanna from Hawaii will be taller next year? Not necessarily. We can’t conclude that.

You should look for this in an answer choice: If the group average rises, then each specific item in the group rises.

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1. This isn’t really flawed. It’s making a prediction based on what the trend has been in the past. But it sticks to the same thing all along: gasoline. It doesn’t switch from a big group to a specific member.
2. Completely different structure. It says either A or B; probably not A, so B.
3. CORRECT. It moves from people under 20 to fourth graders. But fourth graders are just one subgroup. The average for everyone under 20 could rise even if fourth graders’ time stayed the same or decreased.
4. This does mirror the whole and part aspect of it, but it’s not flawed. If the price of ice cream is dependent on the price of sugar, this argument is logical. It’s not the same thing as average of a group = every part of that group.
5. This is also a causal prediction: population group declines → real estate prices decline. No shift from average to individual/subgroup.