## Formal Logic Meltdown

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

Posts: 962
Joined: Sat Dec 12, 2009 12:07 pm

### Formal Logic Meltdown

I think I'm an idiot for never doing any prep for LR besides PT's. I never bought the LR Bible, and I have no idea how to diagram an LR problem because I've never needed to. I usually get parallel reasoning questions just be reading and remembering.

Why focus on LR when you average -1.5 per section and do a lot worse on LG?

But I just got destroyed on PT 61 LR, and it appears almost every problem I missed was a formal logic question. -7 is the absolute worst I've ever done in LR on a PT, even my diagnostic was -6.

It appears there are a lot more of these than there used to be. What should I do with 5 days until the test?

AreJay711

Posts: 3406
Joined: Tue Jul 20, 2010 8:51 pm

### Re: Formal Logic Meltdown

Chillax

suspicious android

Posts: 919
Joined: Tue Feb 09, 2010 4:54 pm

### Re: Formal Logic Meltdown

AreJay711 wrote:Chillax

Yeah, sounds about right. I haven't taken 61 but I'm pretty sure it's not some radical departure from other the other 60. You probably just hit a bad spot.

Flips88

Posts: 15246
Joined: Sun Oct 10, 2010 7:42 pm

### Re: Formal Logic Meltdown

I took in October and went -6 and -7 on my LRs with my format being RC, LR (Experimental), LR, Break, LG, LR. the -7 was my last section and the end of it was loaded some logical inference questions and parallel reasoning that my mind was too fried to deal with. i missed 5 of the last 6 questions. So when studying for December, I've been focusing on LR and on the logical inferences/parallel reasoning/flawed reasoning and refreshing formal logic (which i took as a class as a freshman in college) really helped.

A->B
B->C

A->C

contrapositive: you just negate and switch things. so ~C->~A

Also, helpful is knowing that and/or switch when you do contrapositive so if A->B and C is the equivalent of ~B or ~C->~A

Also, typical trap answers are logical fallacies on inference or logically draw questions.

Affirming the Consequent
A->B
B
Therefore, A

Example:
If it rained, the ground is wet.
The ground is wet.
Therefore, it rained.

The ground could be wet because of sprinklers or something.

Denying the Antecedent
A->B
~A
Therefore B

If it rained, the ground is wet.
It did not rain.
Therefore, the ground is not wet.

the ground could still be wet.

Hope some of this helps in the last days! Good luck!

58932ugahoige

Posts: 75
Joined: Tue Oct 12, 2010 2:23 am

### Re: Formal Logic Meltdown

I don't even know what formal logic is on the LSAT. Are those the "if the above are true, which of the following must be true?" type questions?

I only got 3 wrong between both of 61's LR sections. Rock.

Sadly, when I wrote it in October I blew an easy logic game. Wrote down a rule wrong! 175--->169.

Eugenie Danglars

Posts: 2353
Joined: Wed Jul 07, 2010 12:04 pm

### Re: Formal Logic Meltdown

Shmuckluk wrote:I don't even know what formal logic is on the LSAT. Are those the "if the above are true, which of the following must be true?" type questions?

I only got 3 wrong between both of 61's LR sections. Rock.

Sadly, when I wrote it in October I blew an easy logic game. Wrote down a rule wrong! 175--->169.

Formal logic is stuff like:
All TLS'ers are nerds. Some nerds are friendly. Most TLS'ers are not friendly. All friendly people are popular.

niederbomb

Posts: 962
Joined: Sat Dec 12, 2009 12:07 pm

### Re: Formal Logic Meltdown

Here's a real life example (LSAT=real life?!) from PT 61.

Those who make X express Z. Therefore, X does Y.

D: Any Y is Z. I mis-marked this question as wrong and marked this as the correct answer. WTF?

I spent 45 minutes staring at this problem, until I realized I had gotten it right. B is the answer.

B: To express Z is to do Y. Correct!

2014

Posts: 6027
Joined: Sat Jun 05, 2010 3:53 pm

### Re: Formal Logic Meltdown

niederbomb wrote:Here's a real life example (LSAT=real life?!) from PT 61.

Those who make X express Z. Therefore, X does Y.

D: Any Y is Z. I mis-marked this question as wrong and marked this as the correct answer. WTF?

I spent 45 minutes staring at this problem, until I realized I had gotten it right. B is the answer.

B: To express Z is to do Y. Correct!

That is fundamental formal logic there.

It's just straight up:

X --> Z

Conclusion: X -- > Y
The answer to that one is always going to be Z --> Y because it completes the X --> Z --> Y chain.

I imagine it would be really useful to at least wrap your head around the transitive property and contrapositives before Saturday. Even if the question doesn't look like pure formal logic, the concept comes up quite a bit.

NYC_7911

Posts: 238
Joined: Sat Oct 30, 2010 9:03 pm

### Re: Formal Logic Meltdown

I really don't recommend that you spend any of the last few days before the LSAT trying to cram formal logic into your head. If you've been averaging -1.5, you have what it takes to do FINE. Sounds like 61 was just an anomaly; having taken it, it didn't seem drastically different from any of the other recent tests. Don't let it psych you out!

niederbomb

Posts: 962
Joined: Sat Dec 12, 2009 12:07 pm

### Re: Formal Logic Meltdown

2014 wrote:
niederbomb wrote:Here's a real life example (LSAT=real life?!) from PT 61.

Those who make X express Z. Therefore, X does Y.

D: Any Y is Z. I mis-marked this question as wrong and marked this as the correct answer. WTF?

I spent 45 minutes staring at this problem, until I realized I had gotten it right. B is the answer.

B: To express Z is to do Y. Correct!

That is fundamental formal logic there.

It's just straight up:

X --> Z

Conclusion: X -- > Y
The answer to that one is always going to be Z --> Y because it completes the X --> Z --> Y chain.

I imagine it would be really useful to at least wrap your head around the transitive property and contrapositives before Saturday. Even if the question doesn't look like pure formal logic, the concept comes up quite a bit.

I do know the contrapositive from the LGB. I have no idea what the transitive property is, however. I think I know most of the stuff intuitively; I just don't have a specific strategy, so these questions take me a lot longer to do than they should.

Before PT 61, I usually finished LR with significantly more than 5 minutes to spare, so I'm hoping I will have plenty of time to handle curve balls if I face any. If guess if I don't, I've learned my lesson for next time.

NYC_7911 wrote:I really don't recommend that you spend any of the last few days before the LSAT trying to cram formal logic into your head. If you've been averaging -1.5, you have what it takes to do FINE. Sounds like 61 was just an anomaly; having taken it, it didn't seem drastically different from any of the other recent tests. Don't let it psych you out!

You're probably right. I'm also taking the Beijing test, which is usually a February test from some year past, so I shouldn't be worrying about cutting edge LSAC stuff that won't likely be a factor for me. In fact, if other overseas tests are any indication, I should probably be reviewing mapping games and double-question stimuli.

niederbomb

Posts: 962
Joined: Sat Dec 12, 2009 12:07 pm

### Re: Formal Logic Meltdown

Just took my last PT: PT 38.

-0 LR, -0 LR. -1 RC but -6 LG!!!!!!!!!!!

If it's not one thing, it's another.

Diiizzzzoooo

Posts: 123
Joined: Mon Aug 16, 2010 11:18 pm

### Re: Formal Logic Meltdown

niederbomb wrote:Just took my last PT: PT 38.

-0 LR, -0 LR. -1 RC but -6 LG!!!!!!!!!!!

If it's not one thing, it's another.