Logical Reasoning

PT118 · S1 · Q11 The average cost of groceries

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The average cost of groceries will rise again next month.

Conclusion

Butter and eggs will cost more next month

Evidence

The average cost of groceries will be higher next month

Evaluate

Pretty straightforward — the author thinks that if the average price of groceries is going up, then these two specific groceries (butter and eggs) will also see their price go up.

This is a failure to understand the concept of "average". We don't expect every data point in a set to behave in the exact way the average behaved. This is a Part vs. Whole flaw.

Goal

Look for an argument that abuses the concept of "average" in the same way, or look for an argument that similarly commits a Whole to Part move.

11.

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

  1. The price of gasoline has

    Bad Conclusion Match

    This doesn't go from "average price of gas" to a specific price of gas scenario. If the conclusion said something like, "Therefore, I can expect to pay more for gas at my local station next month." that would be closer to the original.

    7% picked this

  2. Either the government will reduce

    Bad Evidence Match

    The either/or claim right out of the gate makes us want to bail from this one. The flaw this argument commits is simply Probable vs. Certain. Of the two possible options, one is more likely. But the author concludes with certainty that it will happen.

    0% picked this

  3. Correct

    The average amount of time

    Why this is right

    The premise is an average for a big group of things (people under 20). And the conclusion applies that same average idea to a small subset of that group (4th graders). It moves from Whole to Part. Because the trait "watch more tv recently" applies to the Whole, the trait "watch more tv recently" must also apply to each Part.

    Skill tested: Parallel Flaw · how this choice captures the argument's function is the move to repeat next time.

    80% picked this

  4. Since sugar is a major

    Topic Trap Valid Logic

    Back to the grocery store! Beware on parallel questions when it feels like an answer choice is trying to feel similar by being nearby the original topic. This is valid logic, not a Whole to Part assumption. They give us a conditional rule that says "when price of sugar goes up, price of ice cream goes up", so the logic here is sound.

    10% picked this

  5. Real estate prices go down

    Valid Logic

    Just like choice (D), this provides us with a conditional rule (When population of 20-30 years olds goes down, real estate prices go down), which allows the author to validly draw her conclusion.

    2% picked this

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