## PS LGB: December 1996 Game Four - Question 20

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shamirum

Posts: 2
Joined: Thu Aug 15, 2013 2:56 am

### PS LGB: December 1996 Game Four - Question 20

Hello, all! I want to preface this by confirming that I already did a forum search to try and find this answer in a previous post/thread, but it doesn't seem to be in the history. There is one thread that focuses on this exact game, but it deals with diagramming a certain rule and not the question I have.

I am using the PowerScore Logic Games Bible (and hoping it has holy powers). Anyway, on page 79 they present Game Four from the December 1996 exam (this game came up on a list of the top ten hardest games ever, but I still want to master it so I can be prepared for the format, just in case it rears its ugly head my way). Anyway, the analysis of question 20 (page 82), the "defining question" of the game, says that we can use the answer from question 18 and from that "it is certain that either J or G must be the product advertised in week 2." My confusion is based on the wording in question 18 which says the following "could be" the schedule of advertisements. If question 18 is a "could be true" question, how can it be safe to infer that the answer in that question (even though it's global) can apply to a "must be true" question such as question 20 (also global)? I would think the answer in a could be true question is one of at least two or more possibilities, so I'm not seeing the connection that any part of it must be true and can help with a must be true question.

Any insight or direction to help clear my confusion will be greatly appreciated! Really hoping that I'm just missing a simple inference or step. Thanks in advance for your help.

(Please excuse any typos or missing words as I typed this on my phone.)

-S

Jeffort

Posts: 1888
Joined: Wed Jun 18, 2008 4:43 pm

### Re: PS LGB: December 1996 Game Four - Question 20

It's useful for eliminating incorrect answer choices that could be false. If something is not true in the valid hypo from the list question, then that thing certainly doesn't qualify as something that must always be true since we have a valid hypo that shows it isn't something that must be true. The hypo does not by itself prove anything must be true since, as you said, it is just one of what could be many different possibilities allowed by the rules.

Once you use that hypo to get rid of (C) - (E) then you take the next step of trying out a hypo or two to determine which of the remaining answers is something that could be false in order to rule it out and solve by POE.

PS: The version of the LGB you are using is the super old first edition. The page numbers where that game and the explanation is are later in the book in the more recent editions. Instead of using the pdf of the original version that is still floating around in some torrents, you might want to get the current version which is only available in print. It's now twice the size and way more in depth than the original 222 page version. People that just use the LGB they get from a torrent are missing out on half of the stuff that is in the current edition.

10052014

Posts: 590
Joined: Mon Jul 15, 2013 11:12 am

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Last edited by 10052014 on Sun Oct 05, 2014 1:16 am, edited 1 time in total.

shamirum

Posts: 2
Joined: Thu Aug 15, 2013 2:56 am

### Re: PS LGB: December 1996 Game Four - Question 20

Thank you, both. I'm still confused and really want to get this, so I thank you for your time. Why do J and G have to be the products advertised in slot 2 if the list that features them in question 18 is a hypo, not a "must be" list?

As far as the LGB, I completely agree and actually don't mind the cost of the updated book. I am planning on taking a PowerScore course (or maybe even hire one of their tutors) and didn't want to end up with two books. I recently found out that the LGB isn't actually part of the course materials (sort of surprised me), so I'm getting one separately. I still like working on the old one now just because I have the copies and some of my friend's husband's notes, which have been helpful (except for this damned question - I should probably pester him, but liked finding this forum anyway).

Back to my confusion, what am I missing?

Thanks again.

-S

Jeffort

Posts: 1888
Joined: Wed Jun 18, 2008 4:43 pm

### Re: PS LGB: December 1996 Game Four - Question 20

shamirum wrote:Thank you, both. I'm still confused and really want to get this, so I thank you for your time. Why do J and G have to be the products advertised in slot 2 if the list that features them in question 18 is a hypo, not a "must be" list?

As far as the LGB, I completely agree and actually don't mind the cost of the updated book. I am planning on taking a PowerScore course (or maybe even hire one of their tutors) and didn't want to end up with two books. I recently found out that the LGB isn't actually part of the course materials (sort of surprised me), so I'm getting one separately. I still like working on the old one now just because I have the copies and some of my friend's husband's notes, which have been helpful (except for this damned question - I should probably pester him, but liked finding this forum anyway).

Back to my confusion, what am I missing?

Thanks again.

-S

The hypo from the list question doesn't by itself prove that J & G are products that must be advertised in week two. However, if there is a product that must always be advertised in week two, it must be one of those since they are the only two in week two in a hypo we know is valid. Since the question stem of the other one tells us that there is a product that must always be in week two, we know from the valid hypo that it must be either J or G, allowing you to eliminate the other answer choices automatically since they aren't in week two in a valid hypo and therefore are proven that they don't have to be.

As you said, a hypo that could be true doesn't establish things that must be true in all valid hypos. However, that doesn't mean that valid CBT hypos are not useful for solving must be true questions. While it doesn't by itself establish what must be true, any valid hypo that could be true is useful to eliminate incorrect answers on must be true questions by showing that they could be false without violating the rules. Anything listed as an answer choice for a MBT question can be eliminated by a valid hypo where that thing is not true. It's not just whats IN a valid hypo that is useful for POE, its also what is NOT in the valid hypo that is useful for proving that certain things could be false.

While a valid CBT hypo doesn't give you a list of things that always must be true, it does prove that anything not true in the hypo is something that could be false in at least one possible outcome of the game that conforms to all the rules. If something is not true in at least one valid hypo, it is not something that must always be true. J & G are not proven that they must be true by the hypo, rather, they are simply not proven to be things that could be false (like answers C through E) so we cannot use the list question hypo to eliminate them. I'm pretty much repeating myself in different wordings, I hope this makes sense somewhere in this.

Think of answer choices (C) - (E) and compare them to the hypo from the list question. If any of those three products were one that must be advertised in week two, it would have to be in week two in EVERY valid hypo that could be true, including the one from the list question. Otherwise that hypo would not be a valid possibility. Since none of the variables listed in answers (C) - (E) are in week two in the valid hypo, we know that they are not products that must always be in week two, hence they could be false. The CBT hypo eliminates those answers, leaving only (A) and (B), and based on the question stem, one of them is a product that must be true in week two. From there you need to do a little trial and error work to determine which of those two states something that could be false in order to eliminate it and solve the question via process of elimination.

In simple terms: While a could be true hypo doesn't by itself establish which things must always be true, it DOES establish things that could be false in terms of things that are not true in it or another valid hypo. Any valid hypo that doesn't have a certain thing in a certain place proves that that thing doesn't always have to be in that place. Make sense? If something is not true in a valid hypo, then it is something that could be false and therefore not a correct answer to a must be true question.

Conversely, if something must be true globally in a game, it must be true in every valid hypothetical, so finding just one example of a valid possibility where something is not true is sufficient to prove it is something that could be false. Since anything that must be true will be true in every valid hypo, any valid hypo is useful to narrow down answer choices on global MBT questions to the ones that match up with the hypo. Again, it doesn't prove which one must be true, it just narrows it down by getting rid of the ones that don't have to be true since whatever things must be true will be the case in any and every valid possible hypo you can come up with. In the case of this question the list question hypo quickly narrows down the answer to either J or G.

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