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## #25 - Roberta is irritable only when she is tired

• PowerScore Staff
• Posts: 4922
• Joined: Apr 14, 2011
#95472
Good point, Henry! The fact that she lost her keys IS sufficient to prove that she must be tired, so that is NOT a flaw. The only flaw is the Mistaken Reversal, assuming that because she is tired she must be irritable.
queenbee
• Posts: 74
• Joined: Sep 18, 2022
#97996
Hi
here is how I diagrammed the logic:

If R = I --> Tired
If R = L --> Tired

The stimulus said, R lost her keys (R = L), so I took that as R = L --> Tired. So we know that she lost her keys, therefore she must be tired.
It then says, she must be irritable. "Must be" is the indicator of a necessary condition. the only way that could be a necessary condition is if there is a mistaken reversal where If Tired --> R=I.

Based on the diagraming above and on the language used, I selected D.

Answer choice (E) is saying that it took R=I as a necessary condition to be a sufficient condition. But R=I was already a sufficient condition based on the diagraming above.
Thank you
Paul Popa
• PowerScore Staff
• Posts: 48
• Joined: Sep 20, 2022
#98356
Hi Queen,

Great question! So, we're told that regarding Roberta:

I --> T
and
LT --> T.

We're then told that she lost her keys, so we definitely know that she is tired. Her yawning is irrelevant; having lost her keys is sufficient enough to conclude she's tired. But then the argument claims she is "almost certainly irritable." In other words, the argument is incorrectly concluding that because she is tired, then she is probably irritable. But this is a mistaken reversal of the first statement. Robert might not be irritable at all, even though she's tired. Answer choice (E) describes this perfectly: being tired is a necessary condition for being irritable, but the author treated it is a sufficient one.

D is close, because it describes a mistaken reversal, but it refers to the wrong term. The author doesn't assume that because Roberta's tired, that that is why she lost her keys. The author only commits a mistaken reversal once, when they claim that because Roberta is tired, she is probably irritable as well. Hope this helps!

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