## just checking...

Prepare for the LSAT or discuss it with others in this forum.
jfb

Posts: 196
Joined: Tue Feb 03, 2009 1:26 am

### just checking...

F must be played immediately after R, unless G is played earlier than R

this rule would be diagrammed: -RF ---> G...R (if not RF then G before R)

Is that correct??

Philo38

Posts: 344
Joined: Fri Sep 25, 2009 10:21 am

### Re: just checking...

jfb wrote:F must be played immediately after R, unless G is played earlier than R

this rule would be diagrammed: -RF ---> G...R (if not RF then G before R)

Is that correct??

The other way around I think.

Not G . . . R ----> RF

and the contrapositive

Not RF ---> G . . . R

jfb

Posts: 196
Joined: Tue Feb 03, 2009 1:26 am

### Re: just checking...

Thanks for the response. Anyone else??

dub

Posts: 73
Joined: Fri May 21, 2010 9:05 pm

### Re: just checking...

I think you've got it right.

CyLaw

Posts: 1551
Joined: Thu Jul 17, 2008 1:59 pm

### Re: just checking...

Philo38 wrote:
jfb wrote:F must be played immediately after R, unless G is played earlier than R

this rule would be diagrammed: -RF ---> G...R (if not RF then G before R)

Is that correct??

The other way around I think.

Not G . . . R ----> RF

and the contrapositive

Not RF ---> G . . . R

Your contrapositive is exactly what OP has. And contrapositives are equivalent statements to the original in logic.

Edit: And yes OP, I think you have it right. If not RF, then G...R must be true.

Edit: Sorry, and all I meant by my first statement is that you always gain the contrapositive for free, so if OP starts with either !G..R -> RF or !RF -> G...R they will gain the other for free.

jfb

Posts: 196
Joined: Tue Feb 03, 2009 1:26 am

### Re: just checking...

Yes, philo's contrapositive is my original statement, didn't even realize that.

Makes me wonder why would anyone pay for a class when they can just post all of their questions on tls and have them answered within minutes.

Thanks again for the input.

Philo38

Posts: 344
Joined: Fri Sep 25, 2009 10:21 am

### Re: just checking...

Sorry, I wasn't paying close attention. Silly mistake, I read wrong.

Anaconda

Posts: 605
Joined: Sun Jun 06, 2010 3:51 pm

### Re: just checking...

Correct, whenever you see unless simply make the condition modified by unless your necessary condition and negate the rest and make it your sufficient condition. That's exactly what you did!

PS: you also do this for except, without and until. Don't think I've ever seen those before on LG but I'm sure they've appeared on some hard LR questions.

Examples:

Without crack cocaine you will not become a drug addict.

Drug Addict -> Crack cocaine OR No Crack Cocaine -> Not a Drug Addict

(notice how Drug addict becomes positive because of double negation)
---
Joe won't be a loser unless he has no ambition

Loser -> No Ambition or Ambition -> Not a loser
---
The Cubs won't win the World Series until Hell freezes over

Cubs win WS-> Hell freezes over OR Hell doesn't freeze over -> Cubs don't win WS
---

Pretty easy stuff, just remember the basic rule and that it includes unless, without, except and until.

Not knowing what to do with unless, except, without and until can DESTROY someone on logic games, I think that's how LSAC gets roughs up a lot of kids on a few of the easier games as well as some of the much harder in-out games! If I remember correct the Bird in a Forest game had one conditional rule that included "unless." I bet a lot of kids messed up because they wrote that rule down incorrectly!

Balthy

Posts: 665
Joined: Sat Apr 03, 2010 12:28 pm

### Re: just checking...

Just quickly change "unless" to "if not" and go from there. Makes it much easier.

Correct symbolization is -(G>F) --> RF, so you correctly symbolized the contrapositive.