Dinosaur LSAT Logic Game Explanation

Dinosaur LSAT Logic Game ExplainedI would categorize this game as a combination of Selection (In-Out) and Matching.

Basically, we're selecting some variables but not others, and we're associating variables of different types with each other. There's no sequencing or linear aspect to this game.

(Also see my video explanation of this LSAT Logic Game.)

Due to copyright restrictions, I'm forced to leave out the text of the game. You'll need a copy of LSAT PrepTest 57 (the June 2009 LSAT) in order to follow along.

Setup and Main Diagram
We're picking 5 out of 7 dinosaurs. Each dinosaur is one of 4 colors.

7 Dinosaurs: Iguanadon, Lambeosaur, Plateosaur, Stegosaur, Tyrannosaur, Ultrasaur, Velociraptor

4 Colors: Green, Mauve, Red, Yellow


_ _ _ _ _ GMRY (colors)
_ _ _ _ _ ILPSTUV (dinos)

We have definitely have 2 mauves (I didn't know it was a color either).

We also definitely have RS (red stegosaurus - with R above S as a vertical block).

so we can put down:


MMR_ _ = GMRY
_ _ S_ _ = ILPSTUV

Next: I only if G. "Only if" introduces the necessary condition, so we can say "if I -> GI." Because we only care about I's color if it's selected, we can say GI and put it on the side (G above I as a vertical "block")

Same goes for if P -> YP (Y above P as a vertical "block")

V only if U is not = If V-> not U (or U)

Contrapositive: If U -> not V (or V)

This means U and V are never together = V <--/--> U (V double-not arrow U).

If L and U -> ML doesn't happen (ML) or MU doesn't happen (MU). (Again, these should be vertical with M above L and M above U, respectively).

What we have so far should look something like the following picture:


Dinosaur LSAT Logic Game Main Diagram


Inferences and Limited Options / Templates / Possibilities:
Let's take the knowledge that S has to be R, I has to be G, and P has to be Y (if they go, that is).

Indirectly, this is telling us that out of the 7 dinosaurs (ILPSTUV), only L, T, U, and V could ever be M.

However, we know we'll never have both U and V being M. This is because we can never have them both "in" (see the double-not arrow above).

Additionally, we can't have both L and U being M.

The possible combinations of Mauve dinosaurs are, as a result, pretty limited:

LT
LV
TU
TV

We can draw 4 templates using this information. However, we really only need 3, because TU and TV are virtually the same thing. T isn't involved in any other rules, so when T is Mauve and we have one of U/V, U and V are interchangeable - one is in, but the other is out.

This means we can represent the Mauve pairings as really being only possible 3 combinations:

L T
L V
T U/V

Placed on the diagram...

with LT as the Mauve pair:



with LV as the Mauve pair:



with T and one of U/V as the Mauve pair:



This pretty much breaks the game wide open. In each of these templates, the dinosaurs that can be in the remaining two spots are pretty limited.

Below, I've placed the pool of 3 "maybes" in parentheses. Each valid scenario would include any 2 out of those 3.

Template #1:

The "LT Mauve pair" template:



Template #2:

The "LV Mauve pair" template:



Template #3:

The "T and one of U/V Mauve pair" template:


These templates address the V <--/--> U rule and the "LU can't both be Mauve" rule. All we need to keep in mind now when using the templates is that if I is chosen, it will be G, and if P is chosen, it will be Y.


Question 12
Typical question asking which one could be a valid scenario. However, it refers only to dinosaurs and doesn't concern colors, so the templates aren't a huge help here.

Just pick one rule at a time and apply it to the choices.

We always need to have S, so we can eliminate D.
We can't ever have both V and U, so A and E are out.

Choice C lists ILPSU. The problem with this choice is that I, P, and S already have colors associated with them (G, Y, and R, respectively). This would force L and U to both have mauve, which can't happen according to our rules. For this reason, C is out, and B is our answer.


Question 13
If T is out, then we're definitely not going to use the LT or T U/V templates.

We're going to use the LV template, and we're not going to pick T from the parentheses, giving us:





Because the diagram is fully determined, all you have to do now is scan the choices to see which does not appear. Whatever doesn't appear will be your answer. In this case, it's D.


Question 14
Sadly, question 13's diagram doesn't help at all because it doesn't contain GL or YT.

Go back to the templates. GL could never occur in the first 2 templates because L is always M in those templates. However, we could have GL in the third template. In that template, T has to be M, so A works.


Question 15
In the 1st and 3rd templates, T has to be M. However, in the 2nd, it could be Y, so we must be dealing with the 2nd template.

We've never had YT before, so it's time to draw a new diagram:

MMRY_
L V ST_

This leaves GI or YP.

The diagram should look something like the following:


We don't know whether we'll have GI or YP on the 5th pair of slots, but it doesn't matter. MV has to happen, so choice E is the answer.

Question 16
We've never had both I and U before, so we'll need a new diagram.

We don't know whether we're dealing the 1st template or the 3rd, but we know that we're definitely not dealing with the 2nd.

Even without drawing them out specifically to include I and U, we can see that both templates have MT because Templates 1 and 3 are LT and T U/V, respectively. They both include an MT. Making A our answer.

However, for those of you who want to see what I and U being "in" looks like, here it is:

In Template 1, including both I and U would give us:


We still wouldn't know what U is. It could be anything but M. Depending on your preference, you could leave U's color blank, as I did above, or you could do G/R/Y to indicate what color could be.

In Template 3, including both I and U would give us


There obviously isn't room to have both P and L, so we'll have one or the other. If we have P, it'll be Y, but if we have L, we don't know what color it'll specifically be. Again, depending on your preference, you could put G/R/Y to the right of the big slash and box it with L, or you could just leave it empty as I did above.

It doesn't really matter anyway, though, because the question is asking us what must be true across both templates. Both have MT.

Question 17
If we have 2 Gs, what could be true? Well, the bad news is that we could be dealing with any of the 3 templates.

The good news, though, is that we're definitely not going to have P, so each of the three templates is either fully determined or almost fully determined.

Template #1:




Template #2:




Template #3:




In Template #2, it's possible to have a green tyrannosaurus, so B is our answer.

***

Is this a tough game? Absolutely. But is it doable? Yes.

It's not an 8-minute 45-second game for most people. However, the other games in the section (the first one, in particular) are easier in order to balance things out.

Seeing this game explained should ensure Jurassic Park won't give you any more nightmares.



15 comments:

  1. I would like to thank you for explaining the game. In your opinion is this the most difficult game ever till date(90's onwards)?

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  2. I am a Pharmacist and I am telling you I am having a tough time with thinking like this.. It is starting to scare me.. Why is this so difficult for me? Any help out there. Kim

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  3. Question: Wouldn't the following be a better way of solving this game?:
    1) We know there are only 2 "out" spots and U/V must be one of them. Therefore, there is only one "out" spot left. We can make 3 different options where "T" (being the only entity that has no rules to restrict it) can be. "T" is either out, in as mauve color or in as any color.
    If you then follow the rules, you will have 2 complete options and 1 option that is almost complete.
    Try it out and you will see what I mean... Once it is done this way, the game is actually very easy.
    Let me know what you think.

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  4. @6/26 - I don't think this is the hardest game ever, but it's certainly not easy.

    @7/9 Kim - It takes a lot of practice.

    @12/2 Barryb - Your approach works pretty well. I like the creativity.

    However, the approach I covered in this blog post reduces the game's ambiguity more.

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  5. Barry, I like your approach as well. I didn't think of this while doing the game. I just symbolized the rules and drew a rough sketch with 5 slots divided into halves (top for dinosaur type and bottom half for color). Then I filled in the the red steg and the two mauve's and did the rest of the deductions in my head as I went along. It took me roughly 8-9 min's, but if I would have realized that T only had 3 possible options and each of these options created complete or very limited scenarios like you said I could have probably done it in 5-6. Nice deductive reasoning skills!

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  6. Thank you. Your explanations were right on for me. The clarity I sought, you gave.

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  7. This game confused me because I thought that there had to be a dinosaur of every color. I figured this was a key deduction based off of the 1st rule (exactly 2 mauve toys are included). Boy was I caught off guard when I got to question 17 (2 green toys are included)...

    Thanks for the explanation!

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  8. Is it possible to have both U and V out?

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  9. Yes: Green I Red S Yellow P Mauve T and Mauve L

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  10. Barry B, i know this is like a bazillion years later, but i cant get to 3 complete scenarios by using T. Can you or anyone explain?

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  11. @Trudy I'm unable to get to the three scenarios BarryB mentions either, and I'm pretty sure it's because he's wrong. When I tried solving it his way, I ended up with the following three frames:

    NOTE: color of toy in parenthesis.

    1) S(R)L(M)V(M)I(G)P(Y) <-- T is OUT
    2) S(R)L(M)V(M)T(?)I(G)orP(Y) <-- T is IN but not Mauve
    3) S(R)T(M)?(M)?(?)?(?) <-- T is IN and Mauve

    It's possible I've missed some inference here, but I feel confident I'm correct. I originally solved this game with little difficulty using a method similar Steve's. I recommend sticking to his explanation because from what I can tell, BarryB was wrong. You do not end up with two complete frames and one that is almost complete. Hopefully Steve will chime in and confirm here, because if I'm wrong I'd like to know.

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  12. Great! Thank you, Michael! I was feeling very frustrated. I could do Steves, but i was wasting so much time trying to get "complete" scenarios with the T method; thinking that i need to get to the point where i can understand it like those really smart-smart people. I appreciate you taking the time to explain.

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  13. HOLY SHIT! I'm so relieved/aggravated to see this on the list of hardest games, because I took this exam and I was so upset because I had done really well on games on the past. This one just left me stunned. I ended up with a 162, several points lower than I had been performing on practice exams. I was accepted into my top school, but with a lower scholarship that I was hoping for. I plan on retaking the LSAT this June to boost my scores in hopes of more money.

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  14. thanks so much! love this blog...i always start my days looking at this blog! i'm taking the lsat this june and i hope i do well!

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  15. I just took this preptest, and was completely dumbfounded when I came across this question. Thanks for the walkthrough!!

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