Dec 1994 (PT 13) LG Questions 1-6 Forum

[cardsfan04]

How do you approach this question set? When I set it up, I wrote:

F=J
G=/=M
H1-->L1
N2-->G1

I haven't bought the LG Bible yet (because I mistakenly thought I didn't need it), so I might be diagramming this incorrectly. I tried to apply what the LR Bible says about diagramming. I missed a few of these, including question 2. How would you attack question 2 and this question set in general?


I feel like there has to be a quicker way than laying out every possible group list. I might be missing something super obvious too that would make this easier. That has tended to be my biggest problem w/ LGs.

[mickeyD]

First of all, you might want to edit some of that out because you can't really post the exact questions due to copyright laws.

But anyways, this is a tough game, but the key inference involves G/M and the FJ block. Since every researcher has to be placed in one of the two groups, you can reserve one spot in each group for either G or M, by putting a G/M dual option in both groups. Along with that, the H1 ---> L1 rule and it's contrapositive are important.

Now you can make two templates. One with the FJ block in group 1, and one with the FJ block in group 2. It looks like this.

Template 1:
If you place the FJ block in group 1, then H cannot go in 1 because that would bring L to group 1 as well, and exceed the 4 person limit. Therefore H goes in group 2.

1: G/M, F, J __
2: G/M H __ __
(K, N, L)

Template 2:
If you place the FJ block in group 2, then L cannot go in group 2 because if you take the contrapostive of the H1 ---> L1 rule, you get L2 ---> H2. Putting L in group 2 would exceed the 4 person limit. Therefore L goes in group 1.

1. G/M L __ __
2. G/M F J __
(K, N, H)

You can pretty much attack every question using these two templates, only thing to be careful of is where you place N, because it can dictate where G goes. Also by contrapositive, G can dictate where N goes as well.

If this doesn't make sense to you, especially the idea of the contrapositive, I would highly recommend waiting on doing more games until the LG Bible comes in so that way you can start off with a good foundation.

[cardsfan04]

Oops, didn't realize the copyright implications, so I deleted it. That makes a lot of sense. Thanks for taking the time to explain that.

I understand how contrapositives work, and get that if you flip and negate the terms you get "If L is not in group 1, H is not in group 1." I always hate doing that though. Because, while H being in group 2 and L being in group 1 would violate the contrapositive, it doesn't violate the exact terms of the condition. I always want to read it as "If H is in group 1, L is in group 1, but if H is in group 2, L is in group 2 or in group 1." While I understand how to create the contrapositive, I've never taken a logic class. Is the contrapositive ALWAYS considered to be true?

[Icculus]

While I understand how to create the contrapositive, I've never taken a logic class. Is the contrapositive ALWAYS considered to be true?

Yes.

Edit: "while H being in group 2 and L being in group 1 would violate the contrapositive". This is not true the contrapositive states if L is in 2 H is in 2. It does not state if H is in 2 then L is in 2. H could be in 2 and L could be in 1, but L cannot be in 2 and H be in 1.

[cardsfan04]

Ohhhh, you're right. I'm having a slow day today lol. For some reason (because I'm slow) I was reading the contrapositive as essentially meaning H and L always have to be together.