Logical reasoning PrepTest 118 · Section 1 · Question 10

Incorrect. This argument commits the past-to-future flaw, basing a prediction about next month on the trend over the past year. As we noted in our Anticipation step, the argument's premise establishes that prices will go up next month, so this flaw isn't present.

Incorrect. This argument is of a very different structure than the stimulus, using conditional logic. It additionally has degree shifts—from a premise about what is "unlikely" to happen to a conclusion about what "will" happen. Going from a weaker premise to a stronger conclusion is a logical force flaw, not a whole-to-part one.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Flawed Parallel Reasoning

Stimulus Summary:
Average grocery costs will increase, so the price of butter and eggs will increase.

Answer Anticipation:
First, it's important to note a flaw that isn't present in this stimulus—the argument isn't basing a prediction about the future on a past trend. The premise of the argument establishes that the average cost of groceries will increase next month, so that common flaw isn't present here.

Instead, the flaw is going from the overall grocery average—a whole—to individual elements within that list (eggs and butter)—a part of it. This argument is committing a whole-to-part jump in that it assumes what is true of the overall category will also be true of each element in that category. However, it's possible that the cost of butter and eggs will go down or stay the same, and yet the grocery average will increase because of rising prices in other groceries.

One final note—be careful of any answer that goes from a part to a whole! While the two flaws are related, they're not the same, so an answer that makes that jump will be a trap answer.

Answer Explanation:
This answer choice uses what is true of a group (all those under 20) to draw a conclusion about a part of that group (fourth graders). As in the stimulus, it's possible that the overall average TV time could have gone up because the other age groups watched much more TV, while 4th graders watched the same or less. This argument has the same whole-to-part jump.

Key Takeaway:
Know your common flaws for the LSAT! Many questions trade in these flaws, and having them down cold will make it much easier and faster to answer certain questions—especially Flawed Parallel Reasoning.

Incorrect. First, this answer uses something true of the part (sugar) to draw a conclusion about the whole (ice cream). Second, it establishes a premise that creates this relationship—it doesn't just assume that what is true of the part is true of the whole. So it moves in the wrong direction (part to whole) and is valid (since it establishes the relationship is valid).

Incorrect. There's no jump from a part to a whole here, and the argument establishes a relationship that it then applies, so it's another valid argument.