LSAT 67, Logical Reasoning I, Q23, LSATHacks

LR Question 23 Explanation, by LSATHacks

QUESTION TEXT: Three million dollars was recently stolen from the…

QUESTION TYPE: Flawed Parallel Reasoning

CONCLUSION: Some members of the mayor’s staff are suspects.

REASONING: The suspects are former treasury employees, and some members of the mayor’s staff are treasury employees.

ANALYSIS: I’ll make a parallel argument. ‘The suspects are from New York State, and some members of the staff are from New York State.’

That argument obviously doesn’t let us prove that some of the suspects are on staff. Millions of people live in New York State.

Back to the argument. There could be 3,000 former treasury employees, 10 of them are suspects, and 5 of the 3,000 are on staff. There’s no reason the suspects and staff must overlap, it’s a big group.

It’s helpful to draw the structure. I’ve bolded the term in common:

Suspect ➞ Treasury

Mayor’s Office   SOME   Treasury

You can’t connect a ‘some’ statement with the necessary condition of an ‘all’ statement. You can connect with the sufficient condition, but that’s another story.

___________

1. This has two ‘some’ statements. The argument had an ‘all statement’. Apart from that, this makes the same flaw. But B is a better choice.
2. CORRECT. This has an all statement, and a some statement that connects with the necessary condition. We don’t know if the groups overlap.
3. This is a bad argument. It’s like saying: all dogs are pets, all cats are pets, therefore some dogs are cats. But it’s not the same flaw.
4. This is a bad argument (supermarkets never sell all types of food), but it’s a different error.
5. The conclusion here is an ‘all’ statement’. The stimulus concluded with a ‘some’ statement.

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