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Course: LSAT (DEPRECATED) > Unit 1

Lesson 5: Analytical Reasoning – Worked examples

Grouping setup | Given info–could be true | Worked example

Watch a demonstration of one way to approach a "Given info: could be true" question on an grouping setup from the analytical reasoning section of the LSAT. Created by Annie Hollister.

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  • blobby green style avatar for user ligiczhong
    One of the possible groups may like:
    - I, Y, G
    - I, Y, O
    - I, Y, W
    Which satisfy the choice “all 3 group have yellow in them”. But why we cross (C) out?

    Further more, why the combination “R, W, O” must in one of the costumes?
    (0 votes)
    Default Khan Academy avatar avatar for user
    • duskpin sapling style avatar for user Tom Walter
      RWO must be an answer because R must be used at least once in one of the costumes, and W and O are the only possible colors to go with it.

      Since we know that R is used in one of the costumes, we can put it in the top slot of the first costume (though it doesn't really matter if it's the first one or a different one, this isn't an ordering problem).

      Then we look at which letters can go with red. We know from rule 4 that G and I can't go with R, so that leaves O, W, and Y, to choose from. Rule 2 tells us that Y must be paired with I, which is incompatable with R, so the only options left to pair with R, are W and O. Leaving us with a definite RWO combinaton.
      (5 votes)
  • leafers seed style avatar for user wrfleishman
    The top of the question is cut from the screen.
    (0 votes)
    Default Khan Academy avatar avatar for user

Video transcript

- [Instructor] This question asks "Which one of the following could be true?" In other words, which of the following doesn't violate any rules of the setup? With this question, we should be able to rule out wrong answers based on what we've deduced from the information given in the setup. So let's think about what we know. Any costume that has indigo in it must have yellow in it and likewise any costume that has yellow in it must have indigo in it. And any costume that has red in it can't have either indigo or green in it. This means that any costume that has red in it also can't have yellow in it. So we can rule out E, which says that at least one of the costumes has both red and yellow in it. We also know that red can't be paired with indigo, green, or yellow, and there are only 6 colors. That means that the only colors that red could be paired with are orange and white, and since each costume has 3 colors, that means that red, orange, and white must all be together. So we've figured out that one of the costumes is red, white, and orange and since no two costumes can have the same color combination and this is the only color combination that could include red, this means that there's only one costume that can have red in it. This lets us rule out a lot of choices. For instance, we know that only one costume can have red in it, so we can cross out C, and that the costume that has red in it can't have green in it, so we can cross off A. We also know that the costume that has red in it can't have yellow in it, because yellow is paired with indigo, and red can't be paired with indigo, so we can cross off B. That means that there's only one choice left: D, exactly one of the costumes has orange in it. Let's just quickly test this out. We've figured out that the costume that has red in it must have orange in it, so if exactly one of the costumes has orange in it, it's this one. So we just want to make sure it's okay for neither of the other two costumes to have orange. This seems fine. For instance, if this costume is indigo, yellow, and green, then this costume is indigo, yellow, and white. This doesn't violate any of the rules of the setup, so it looks like D is perfectly fine.