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Course: LSAT (DEPRECATED) > Unit 1

Lesson 5: Analytical Reasoning – Worked examples

Grouping setup | Overview | Rules and deductions

Watch a demonstration of how to approach a grouping setup on the analytical reasoning section of the LSAT.

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  • blobby green style avatar for user John Furagganan
    The explanation here does not make any sense. There is no rule that says red cannot be paired with yellow. And I don't understand why the second and third costume color combination cannot have red. The explanation here is so vague.
    (3 votes)
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    • blobby green style avatar for user Adri Ana
      The rules indicate that yellow must always be paired with indigo. Since red cannot be paired with indigo but yellow must always be paired with indigo red cannot be paired with yellow. Imagine designing a costume that has red, yellow in it. Looking back at the rules we see that since there is yellow there needs to be indigo in it as well. But this contradicts the rule that red cannot be with indigo. This means that if a costume with three colours has red, by process of elimination we must have orange and white because no other colour fits. Therefore red only has one possible colour combination and order doesn't matter so ROW, RWO, WOR, etc are not different pairings. Since red has only one pairing and there can be no repeat pairings the other pairings cannot have red in them.
      (12 votes)
  • blobby green style avatar for user Brittany Warren
    The last rule seems to be misunderstood. @. If R then ~I AND ~G. The instructor had If R then ~I or ~G.
    (2 votes)
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  • starky seedling style avatar for user Marietjie
    Last comment was 5 years ago wow where is the people of 2024
    (1 vote)
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Video transcript

- [Instructor] This setup has to do with the colors of three costumes. First we'll want to look at the basic structure of the setup so we can understand what type of questions these are and how we might represent it in a diagram. Here's what the setup says: "A costume designer has been asked to put together "exactly three tricolored costumes, "choosing among six colors - green, indigo, "orange, red, white, and yellow. "Each of the six colors must appear "in at least one of the costumes. "The costumes are to be designed according "to the following requirements." Before we look at the requirements, let's think about what this tell us. The setup asks us to group six colors among three costumes and there's nothing in the setup to suggest that the order of the costumes matter, so it looks like this is a straightforward grouping scenario. What information do we have? Well, a designer is putting together three tri-colored costumes, so three costumes of three colors each, so here's one way we might represent that. There are three sets of three. And if we want to label these one, two, and three, we can but just don't get confused. The order doesn't matter but let's think, there are three costumes of three colors each. We know that there are six colors, green, indigo, orange, red, white, and yellow. Now let's look at the requirements. "No two costumes can have the same color combination." There isn't a great way to represent this in the diagram so maybe let's just make a note to ourselves saying something like, "All different," just so we'd remember that. Okay, "any costume that has indigo in it "must also have yellow in it." So indigo, then it's got yellow in it. "Any costume that has yellow in it "must also have indigo in it," so we can just add this here. Indigo, then it has yellow in it and if it has yellow in it, then it has indigo in it. "If a costume has red in it, "then it can have neither indigo or green." So if it's got red in it, then it doesn't have either of these, not indigo or green. Okay, let's see if we can make any inferences from this. Well, if any costume with indigo must have yellow and any costume with yellow must have indigo, this is another way of saying that indigo and yellow are a pair. So this might be an easier way of remembering that indigo and yellow are a pair. So let's erase this, just so we can see that these two always go together. The fourth rule says that red can't be paired with either indigo or green. Since indigo and yellow are a pair, this also means that red can't be paired with yellow. So you could write this. Say it like this. Since there are only six colors though, this means that the only colors left that could be with red are white or orange and each costume is three colors. So if there are only two colors left that could be with red, white and orange, this means that one of the costumes must be red, white, and orange. Since the order doesn't matter, let's just put this in. We know that one of the costumes is going to be this order. We also know that since indigo and yellow are a pair, then another one of the costumes must have these two somewhere. So again, the order doesn't matter, so let's put this in somewhere else. And since no two costumes can be the same, and there's only one possible color combination with red, that means that only one costume can have red in it so we could even just make a little note here saying, "These two definitely don't have red in them." Okay, that's a lot of information, but it should put us in a great position to be able to answer the questions.