#13 - Local, Could Be True

[Dave Killoran]

Complete Question Explanation
(The complete setup for this game can be found here: lsat/viewtopic.php?t=1891)

The correct answer choice is (C)

The question stem defines the size of the group: four CDs are for sale, each of them used. As used pop is on sale from the first rule, the question setup appears as follows:

Jun 00__M12_game#2_L11_explanations_game#4_#13_diagram_1.png

Thus, used jazz, used opera, used rap, and used soul are the four contenders for the three remaining spaces. As only one of these four can be removed from the pool, we can eliminate answer choice (E) immediately because it attempts to remove two of the remaining types of used CDs.

The best approach at this point is to consider what happens when certain used CDs are eliminated:
If used jazz is not on sale, then neither type of jazz is on sale, and the fourth rule is enacted. Consequently, new pop would have to be on sale, which is impossible given the constraints of the question stem. Thus, used jazz must be on sale:

Jun 00__M12_game#2_L11_explanations_game#4_#13_diagram_2.png

Answer choices (A) and (D)—both of which indicate that used jazz is not on sale—can thus be eliminated.

If used opera is not on sale, a problem arises because of the rules involving the other CDs. When used opera is not on sale, both used rap and used soul must be on sale. But, this creates a problem because according to the last rule, if either type of rap is on sale, then no soul is on sale. Thus, used opera must be on sale, and answer choice (B) can be eliminated.

Hence, by process of elimination, answer choice (C) is proven correct.

[adlindsey]

I was reviewing this problem even though I got it correct. I solved this one differently and a bit faster. But, I'm not sure if I just lucked out? I already knew PU was on sale, so I looked for three other used ones out of the other four used CDs. I then looked at the rules to see which ones would allow three, or not allow one, of the remaining four. I saw the contra-positive of the 5th rule. S ~RN + ~RU and came to C.

[David Boyle]

I was reviewing this problem even though I got it correct. I solved this one differently and a bit faster. But, I'm not sure if I just lucked out? I already knew PU was on sale, so I looked for three other used ones out of the other four used CDs. I then looked at the rules to see which ones would allow three, or not allow one, of the remaining four. I saw the contra-positive of the 5th rule. S ~RN + ~RU and came to C.

Hello adlindsey,

That was a clever way to do things, though there may be others. ...Yes, the interesting antipathy between rap and soul in this game can help solve the game quicker!

Hope this helps,
David

[rpark8214]

Hi,
Would another possible correct answer to this question (if listed) be "used soul is not on sale?" Much appreciated!

[Kristina Moen]

Hi rpark,

If used soul is not on sale, then used rap, used jazz, used pop, and used opera would be on sale. With that list, you can quickly scan the rules.

Rule #1: Used pop is on sale. But new opera is not, so we're good!
Rule #2: Both types of pop are not on sale (only used pop), so we're good!
Rule #3: Used jazz is on sale, so we're good!
Rule #4: Used rap is on sale... but used soul is not, so we're good!

So yes, I believe that could be a correct answer to this question.

[Oneshot06]

Hi, I got this q. right, however, I was down to a.) and c.) and was able to make c.) work so I went with it, but I'm still a little stuck on the conditional relationship of J.

I reasoned since PN HAS to be not on sale (given that only 4 used CDs are on sale), the contrapositive of rule 4 places JU on sale, since either JU or JN have to be on sale and because JN is out, JU is in. The part I don't fully understand is from the explanation for this answer "If used jazz is not on sale, then neither type of jazz is on sale, and the fourth rule is enacted." I get the latter part once the rule is applied, but not the former part.

When I write it out: -JU -JU and -JN it doesn't make sense to me because the rules don't say we can't have both JU and JN not on sale....could you please help me make sense of this?

The other question I have is in regards to the set up for rule #3:

"If both types of jazz are on sale, then no rap is"

Diagrammed: JU+JN -RN + -RU , contrapositive RN or RU -JN or -JU

In terms of the conditional relationship, If I have RN or RU on sale, then I DO NOT have JN AND JU on sale. "NO JN or NO JU" really means BOTH are out? I still get a little fuzzy on the "and" and "or" and if you could provide a simple example so the understanding sticks, vs. just the mechanical notation of the rule, it would be greatly appreciated.

Thank you!

[Adam Tyson]

The inference that is tripping you up on this question is based on the specifics of the local question, and not solely on the original rules, Oneshot. The question is telling us that there are no new CDs on sale, only used ones ("exactly four of the five types of used CDs are the only CDs on sale"). That means that new Pop, new Jazz, new Soul, new Rap, and new Opera are all "out". If used Jazz is not on sale, then IN THIS CASE it means that neither used nor new Jazz is on sale. It's not a global rule, but local for this question!

Now with that info we can apply the global rules and see that with both types of Jazz out, then new Pop has to be. But it cannot be, because only used CDs are in the sale, and the new ones have to be out! That's why A cannot be true - it would result in a conflict between the global rules and the local restriction placed on this question.

As to the third rule, you diagrammed it correctly, but the "or" means "at least one", and does not require both to be out. So if any type of Rap is on sale, then at least one type of Jazz is not on sale. Later on in the rules you'll find out that it has to be exactly one is out and the other one is in, because if you had both out then you have to have new and used Pop, which will then require that all the Soul is in, and you'll have a problem because you can never have Rap and Soul together on sale. But that's an inference for another question!

Again, "or" means "at least one". That's the key here. I hope that helps!

[Oneshot06]

Thanks for clarifying Adam. Makes perfect sense now.