Either/or multiple condition

thegarciab0y
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Joined: Sat Nov 13, 2010 6:32 pm

Either/or multiple condition

Postby thegarciab0y » Thu Nov 25, 2010 1:03 am

Correct me if I am wrong, but when taking the contrapositive of an “or” multiple condition statement, the contrapositive translates the “or” into an “and”.
i.e.: If he gets approved for a loan “or” gets a scholarship, he will go to college.
AL= Approved for a loan
S=Gets a scholarship
GTC=Go to college
AL
“Or” -> GTC
S
Contrapositive
~AL
~GTC -> “And”
~S
The reason why I ask is because I just purchased the Powerscore Logical Reasoning Bible Workbook and started working in it today, and they have already made this mistake twice and I have only gotten to page 15. In the LRB it clearly states that when taking the contrapositive the “or” -> “and” …..”and”->”or”.
This makes a total of 3 errors so far by page 15 in the workbook, I really hope this is not the case with the entire book, because I have a lot of faith in Powerscore and something like this needs to be clarified for me.
-For some reason I couldn't get the ~AL and the ~S to line up on the contrapositive but I'm sure you guys could have figured that out....

dakatz
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Joined: Sat Mar 29, 2008 4:19 pm

Re: Either/or multiple condition

Postby dakatz » Thu Nov 25, 2010 1:26 am

You are making mistakes, not the book. But thats totally normal for someone just starting with this stuff. The conditional should be:

If AL or S ---> GTC

Contrapositive: If no GTC ---> No AL AND No S

thegarciab0y
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Joined: Sat Nov 13, 2010 6:32 pm

Re: Either/or multiple condition

Postby thegarciab0y » Thu Nov 25, 2010 1:33 am

That's exactly what I said........ ~ meaning "cross-out" or opposite

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JazzOne
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Re: Either/or multiple condition

Postby JazzOne » Thu Nov 25, 2010 1:36 am

thegarciab0y wrote:That's exactly what I said........ ~ meaning "cross-out" or opposite

Take a look at the OP. Your formatting got messed up. I think your logic is correct, but I really doubt the Bible is full of errors.

dakatz
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Re: Either/or multiple condition

Postby dakatz » Thu Nov 25, 2010 1:37 am

thegarciab0y wrote:That's exactly what I said........ ~ meaning "cross-out" or opposite


The way you have it written now, you have an arrow pointing to the word "and" which makes no sense. So perhaps you should go back and format it properly if you want to convey correctly the problem. Write it linearly, not stacked.

thegarciab0y
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Re: Either/or multiple condition

Postby thegarciab0y » Thu Nov 25, 2010 1:39 am

Oh and the third mistake... correct me if I am wrong.
It states "The proposal will pass if and only if there is no opposition"
Now I have been studying for the lsat a little too long not to know what "if and only if" means. Its the double arrow right?
So I wrote PP <---> NO PP=Proposal pass and NO= no opposition
The book writes the answer like so...
PP <---> O and says PP=Proposal pass and O=opposition.
Wouldn't it be "no opposition"??? Why would they negate it, I simply don't understand.

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JazzOne
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Re: Either/or multiple condition

Postby JazzOne » Thu Nov 25, 2010 1:40 am

thegarciab0y wrote:Oh and the third mistake... correct me if I am wrong.
It states "The proposal will pass if and only if there is no opposition"
Now I have been studying for the lsat a little too long not to know what "if and only if" means. Its the double arrow right?
So I wrote PP <---> NO PP=Proposal pass and NO= no opposition
The book writes the answer like so...
PP <---> O and says PP=Proposal pass and O=opposition.
Wouldn't it be "no opposition"??? Why would they negate it, I simply don't understand.

Once again, I agree with your logic, but I don't own the Bible. Your diagram is correct.

PP <--> ~O
~PP <--> O
Last edited by JazzOne on Thu Nov 25, 2010 1:41 am, edited 1 time in total.

thegarciab0y
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Joined: Sat Nov 13, 2010 6:32 pm

Re: Either/or multiple condition

Postby thegarciab0y » Thu Nov 25, 2010 1:41 am

-For some reason I couldn't get the ~AL and the ~S to line up on the contrapositive but I'm sure you guys could have figured that out....

Meaning the ~AL and the ~S are above and below the "and" on the contrapositive, just couldn't get them to line up, tried almost everything.

dakatz
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Joined: Sat Mar 29, 2008 4:19 pm

Re: Either/or multiple condition

Postby dakatz » Thu Nov 25, 2010 1:44 am

thegarciab0y wrote:Oh and the third mistake... correct me if I am wrong.
It states "The proposal will pass if and only if there is no opposition"
Now I have been studying for the lsat a little too long not to know what "if and only if" means. Its the double arrow right?
So I wrote PP <---> NO PP=Proposal pass and NO= no opposition
The book writes the answer like so...
PP <---> O and says PP=Proposal pass and O=opposition.
Wouldn't it be "no opposition"??? Why would they negate it, I simply don't understand.


We still have no clue what the first 2 "mistakes" are, but sure, lets focus on this one to see what the confusion is. You are correct that "if and only if" is a double arrow (called bi-conditional since each factor is both necessary and sufficient for the other).

So the proposal will pass (PP) if and only if there is no opposition (NO):

PP <---> NO (Just as you wrote it, though I'd be more inclined to say --O as to avoid using a double-negative in the contrapositive)

You are correct that the contrapositive would just be the negation of the two factors:

--PP <---> --NO (Which, according to you is not how the book has it)

Yet something is making skepitcal that the book has error after error yet I didn't come across any of these and constantly used the book to tutor LSAT students. You are typing this verbatim? What page are you working off?
Last edited by dakatz on Thu Nov 25, 2010 1:45 am, edited 1 time in total.

thegarciab0y
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Re: Either/or multiple condition

Postby thegarciab0y » Thu Nov 25, 2010 1:44 am

It's actually the Bible Workbook, the Powerscore workbook for LR that Just came out literally this month I'm almost positive. It has all the set-ups and explanations for 3 of the PT's LR sections.
--LinkRemoved--
Who would have thought that Powerscore would have made these mistakes. I tried to call them and ask and got the run around and never actually got to speak with somebody.

dakatz
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Re: Either/or multiple condition

Postby dakatz » Thu Nov 25, 2010 1:47 am

thegarciab0y wrote:
-For some reason I couldn't get the ~AL and the ~S to line up on the contrapositive but I'm sure you guys could have figured that out....

Meaning the ~AL and the ~S are above and below the "and" on the contrapositive, just couldn't get them to line up, tried almost everything.


Well then in that case you have it exactly right. I'm not sure how the book has it, but I can't say you are at all incorrect. Makes me pretty anxious to see this book for myself. Usually, when someone claims to see a series of "errors", it is really just a reflection of their own misunderstandings. Yet you are totally right in your interpretation.

thegarciab0y
Posts: 60
Joined: Sat Nov 13, 2010 6:32 pm

Re: Either/or multiple condition

Postby thegarciab0y » Thu Nov 25, 2010 1:51 am

I totally agree usually when I get answers wrong consecutively and I’m scratching my head it’s just because I’m too tired or something, but I brought the bible with me just in case I needed to refer back to it, since the LRB Workbook is supposed to be just putting the LRB concepts to work, and within the first 15 pages it has you do nothing but contrapositives and assumption negation drills and stuff like that to warm you up I guess. I haven’t even gotten to the good stuff yet and I’m sitting here like wtf??, somebody rushed to publish a book….




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