Is this contrapositive correct?

ComatoseClown
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Is this contrapositive correct?

Postby ComatoseClown » Fri May 27, 2011 2:34 pm

I wanted to clarify if my understanding of the contrapositive to this constraint is correct?

1) If Adam and Claire are selected, then Ted is selected.

Contrapositive, in words:
If Ted is not selected, then [only] Adam isn’t selected (and Claire could still be selected)
OR
If Ted is not selected, then [only] Claire isn’t selected (and Adam could still be selected)
OR
If Ted is not selected, then neither Adam nor Clarissa are selected {in other words “both Adam and Clarissa are not selected”}

(notated, respectively):
-T —> -A
OR
-T —> -C
OR
-T —> -A and -C


Is the above understanding completely correct, and particularly is what is in the parentheses completely correct?



2) For the constraint "If G is selected, then S or V is selected": Could S and V BOTH potentially be selected if G is selected; or is it limited to just one of S&V?


Thanks for taking the time to read,
cc

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Ginj
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Re: Is this contrapositive correct?

Postby Ginj » Fri May 27, 2011 2:38 pm

If Adam and Claire are selected, then Ted is selected.

Contrapositive: If Ted is not selected, Adam or Claire isn't selected.

flexityflex86
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Re: Is this contrapositive correct?

Postby flexityflex86 » Fri May 27, 2011 2:40 pm

Ginj wrote:If Adam and Claire are selected, then Ted is selected.

Contrapositive: If Ted is not selected, Adam or Claire isn't selected.

This is the correct.

You could still have one of them or have either.

You should know this if you're taking the June test....

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bport hopeful
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Re: Is this contrapositive correct?

Postby bport hopeful » Fri May 27, 2011 2:43 pm

I thought this read "contraceptive" and came here to tell you that if you had to ask if it were correct (whatever it means for contraceptive to be correct), then it likely isnt.

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boosk
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Re: Is this contrapositive correct?

Postby boosk » Fri May 27, 2011 3:40 pm

ComatoseClown wrote:[b]1) If Adam and Claire are selected, then Ted is selected.
cc



If Ted is NOT selected then either Adam or Claire or both are NOT selected

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BrightLine
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Re: Is this contrapositive correct?

Postby BrightLine » Fri May 27, 2011 4:33 pm

Ginj wrote:If Adam and Claire are selected, then Ted is selected.

Contrapositive: If Ted is not selected, Adam or Claire isn't selected.


Right, just make sure you know that in LSAT world it means Adam or Claire or Both are not selected. It was easier for me to think of it as if Ted is not selected then it is not the case that both Adam and Claire are selected.

As far as diagramming it -T -> -(A + C)

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BrightLine
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Re: Is this contrapositive correct?

Postby BrightLine » Fri May 27, 2011 4:40 pm

ComatoseClown wrote:


2) For the constraint "If G is selected, then S or V is selected": Could S and V BOTH potentially be selected if G is selected; or is it limited to just one of S&V?





G -> S v V If G then either S or V or both are selected
Contrapositive -S + -V -> -G




The basic rule for contrapositive is to that you move everything from before the -> to after. And when you do so, you negate evething. So in the above example G become -G , S become -S, V becomes -V and OR( symbolized with "v") becomes AND(symbolized with +)

ComatoseClown
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Re: Is this contrapositive correct?

Postby ComatoseClown » Fri May 27, 2011 6:02 pm

If Ted is NOT selected then either Adam or Claire or both are NOT selected


So then I assume everything I wrote in the original post is correct, right? I understand that the above quote is how the contrapositive to this is normally written -- the reason I wrote it out in longhand statements in my OP is because I wanted to know if the understanding was correct. So all the statements are correct, yes?

AFS
Posts: 61
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Re: Is this contrapositive correct?

Postby AFS » Fri May 27, 2011 11:48 pm

bport hopeful wrote:I thought this read "contraceptive" and came here to tell you that if you had to ask if it were correct (whatever it means for contraceptive to be correct), then it likely isnt.


That's what Adam and Claire were missing and that's how Ted came to be selected into the world. :wink:

SanDiegoJake
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Joined: Mon Mar 07, 2011 3:17 pm

Re: Is this contrapositive correct?

Postby SanDiegoJake » Thu Jun 02, 2011 2:59 pm

ComatoseClown wrote:I wanted to clarify if my understanding of the contrapositive to this constraint is correct?

1) If Adam and Claire are selected, then Ted is selected.

Contrapositive, in words:
If Ted is not selected, then [only] Adam isn’t selected (and Claire could still be selected)
OR
If Ted is not selected, then [only] Claire isn’t selected (and Adam could still be selected)
OR
If Ted is not selected, then neither Adam nor Clarissa are selected {in other words “both Adam and Clarissa are not selected”}

(notated, respectively):
-T —> -A
OR
-T —> -C
OR
-T —> -A and -C


Is the above understanding completely correct, and particularly is what is in the parentheses completely correct?



2) For the constraint "If G is selected, then S or V is selected": Could S and V BOTH potentially be selected if G is selected; or is it limited to just one of S&V?


Thanks for taking the time to read,
cc


#1: Completely correct.
#2: Both could potentially be selected.




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