LSAT 138 | Section 4 | Logical Reasoning: Q1

LR Question 1 Explanation

QUESTION TEXT: Jim’s teacher asked him to determine whether a sample…

QUESTION TYPE: Flawed Reasoning

CONCLUSION: Jim thought the substance had iron.

REASONING: Magnets attract iron, and the magnet attracted the substance.

ANALYSIS: This argument makes a sufficient/necessary error. Jim thought that iron was the only thing that the magnet would attract. But it’s possible that there are other substances that could be attracted by magnets.

Note that since this is a conditional logic question, you could draw it. However, I use drawings sparingly. Here, to me, the reversal is clear, but I’m not sure how to draw it. I’d have to spend a few minutes figuring it out. The point of diagrams is to make you go faster. You don’t get points for making them, so you should only make them if they help.

As a rule of thumb, if a flaw question uses a conditional statement, then that question will have a sufficient/necessary error. Once you know to look for this error, there’s no need to draw: it will just slow you down.

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1. This contradicts the stimulus. The stimulus said that “magnets attract iron”, which means they always attract iron. As a rule, you shouldn’t try to contradict the stimulus. But the real reason this isn’t correct is that it doesn’t pinpoint Jim’s error: he thought that only iron could be attracted by magnets, which is wrong.
2. So? We’re only talking about magnets. Though if this had said “magnets attract other objects besides iron”, then it would have been correct.
3. The question gives no information about magnet orientation.
4. CORRECT. If this is true, then the magnet could have attracted the substance even if the substance had no iron.
5. We don’t know how strongly the substance was attracted, so this has no impact on the argument.