Q17 - Everyone who is excessively generous

[ashleydymond]

I'm not sure if I can post a question here or not. But I'm a bit stuck on the formal logic of Q#17 from SuperPrep B (Feb1999).

THis is how I see it diagrammed:
"Everyone who is excessively generous is not levelheaded":
EG ---> -LH

"and no one who is levelheaded is bold."
-LH ---> B

Combined Chain Results:

EG---> -LH --- > B

Inferences: EG----> B, -B---> LH---> -EG

But how is answer D correct? How is LH -->-B & -EG

I don't see -B as the necessary condition that yields answer D as the answer choice.

Am I diagramming something incorrectly? Any explanation would help. I'm not able to deduce something that seems pretty simple. I referenced the answer in my SuperPrep book, but they don't show any diagramming. Thanks.

[ManhattanPrepLSAT1]

You're absolutely welcome to post questions here. Sorry about the delay in getting back to your post. It's actually a very good question, so thanks for bringing it to the forum!

The error is in your notation of the second constraint. It should read:

LH ---> ~B


Think of answer choice (D) as blending the two statements in the stimulus in a similar way to the following example.

A ---> B
A ---> C

Therefore we can infer

A ---> B + C

Hope that helps! Let me know if that doesn't answer your question.

[farhadshekib]

I'm not sure if I can post a question here or not. But I'm a bit stuck on the formal logic of Q#17 from SuperPrep B (Feb1999).

THis is how I see it diagrammed:
"Everyone who is excessively generous is not levelheaded":
EG ---> -LH

"and no one who is levelheaded is bold."
-LH ---> B

Combined Chain Results:

EG---> -LH --- > B

Inferences: EG----> B, -B---> LH---> -EG

But how is answer D correct? How is LH -->-B & -EG

I don't see -B as the necessary condition that yields answer D as the answer choice.

Am I diagramming something incorrectly? Any explanation would help. I'm not able to deduce something that seems pretty simple. I referenced the answer in my SuperPrep book, but they don't show any diagramming. Thanks.

I'll also show you my diagram:

Sentence 1:
EG ---> ~ LH;
LH --> ~ EG.

Sentence 2:
LH --> ~B

The "no one" actually modifies the necessary condition.

So, we know that LH --> ~ EG + ~ B. Hence, D is correct.

Here is a great vid on this relationship (Fast forward to 1:17).

http://www.youtube.com/VelocityLSAT#p/u/10/wQIikUQVB0I