Substitution Questions

[Mark83]

In logic games what is the best way to approach substitution questions like, "Which of the following if substituted for X, would have the same effect in determining the assignment of managers?"

I always have the most difficulty with these questions because I'm never sure how to begin approaching them.

[Adam Tyson]

Great question, Mark83, as a lot of students dread those questions and see them as among the most challenging type in LG. There is, however, a simple way to look at them, and that is to paraphrase them this way: which answer choice would you diagram exactly the same way as the rule you are getting rid of? The same representation, the same inferences, nothing left out and nothing new. Focus on how you would diagram the answer, and that often makes at least a few of the answers immediate losers.

For example, take a look at question 7 in the September 2017 games section. We need a rule that will be diagrammed the same way as "S must be in the West Theater." We likely would have diagrammed that with a "not law" to the right of the row for the East Theater. Which of the answers would make us do the same?

Answer A is about sequencing. We would diagram it with a sequencing notation, not a not-law. That's out.

Answer B creates a not-block, not a not-law. That's out.

(so far I haven't actually diagrammed anything, I've just though about how I might diagram these answers and whether it might be the same as what I did with the original rule being replaced)

Answer C: This is a little different than the previous answer, because I know where U is - it's in the East Theater. So S cannot be in the East Theater. That was my prephrase! Contender.

Answer D: I would diagram this rule with a not-block, not a not-law. Loser.

Answer E: Another sequencing rule, which is not what I am replacing. Loser.

C must be correct, and no diagram needed! Just think about HOW to diagram the new answer, and pick the one that would be diagrammed the same way as what you are replacing. A much simpler way to conceptualize these questions, isn't it?

Give that a try and let us know if that helps you get your head around these otherwise challenging questions. Good luck!

[Mark83]

Great question, Mark83, as a lot of students dread those questions and see them as among the most challenging type in LG. There is, however, a simple way to look at them, and that is to paraphrase them this way: which answer choice would you diagram exactly the same way as the rule you are getting rid of? The same representation, the same inferences, nothing left out and nothing new. Focus on how you would diagram the answer, and that often makes at least a few of the answers immediate losers.

For example, take a look at question 7 in the September 2017 games section. We need a rule that will be diagrammed the same was as "S must be in the West Theater." We likely would have diagrammed that with a "not law" to the right of the row for the East Theater. Which of the answers would make us do the same?

Answer A is about sequencing. We would diagram it with a sequencing notation, not a not-law. That's out.

Answer B creates a not-block, not a not-law. That's out.

(so far I haven't actually diagrammed anything, I've just though about how I might diagram these answers and whether it might be the same as what I did with the original rule being replaced)

Answer C: This is a little different than the previous answer, because I know where U is - it's in the East Theater. So S cannot be in the East Theater. That was my prephrase! Contender.

Answer D: I would diagram this rule with a not-block, not a not-law. Loser.

Answer E: Another sequencing rule, which is not what I am replacing. Loser.

C must be correct, and no diagram needed! Just think about HOW to diagram the new answer, and pick the one that would be diagrammed the same way as what you are replacing. A much simpler way to conceptualize these questions, isn't it?

Give that a try and let us know if that helps you get your head around these otherwise challenging questions. Good luck!

Thanks Adam. I'm excited to try this out. Is there an index where I can find the specific question type among past logic game question sets to practice with?

[Adam Tyson]

Sadly, no, we don't have an easy index like that. Try just scanning through the games you have and looking each time at the last question of each game (because historically, questions like that have been saved for the end of the game rather than messing with us in the middle.

Here's another tip for attacking those questions - focus on the inferences. If the rule you are replacing gave you a particularly clear and powerful inference, then perhaps the new rule will describe that inference? Imagine this scenario:

Exactly one of R and P must be selected
If M is selected, R must also be selected

From these two rules, we would get a very clear and powerful inference that M and P cannot be selected together, because M requires R, which knocks out P (exactly one of R and P means you cannot have both).

Now, if we were asked to eliminate the second of those rules and substitute an answer choice for it to have the same effect, we could try looking for that inference. A rule that said "If M is selected, P is not selected" would have the same effect on the game, because we would then have to infer that if M was selected, R would have to be!

Add that to your toolbelt, and give it a go. Good luck!

[Vy5]

Hi Adam,

Thank you for sharing this very helpful method. For this question, do you still rule out or eliminate the other answers? I find that usually two or three may be eliminated through past work and another answer choice by using the rule along with the others and seeing if it would violate the original conditions.

[Dave Killoran]

Sadly, no, we don't have an easy index like that.

Actually, we do, and have for years! It's at: https://www.powerscore.com/gamesbible/l ... /index.cfm

[menkenj]

Thank you so much for the explanation in this thread, I found it a helpful supplement to the discussion in the Bible. I appreciate the index as well. I find it temping to attack these games but worry about spoiling PTs. Is there harm in doing so?

[Adam Tyson]

Not at all, menkenj! Just do so sparingly. If you want to tackle that May 2020 Flex test as a full PT, for example, then don't do that Rule Sub question by itself. Practice throughout your LSAT prep is about doing some questions pulled from old tests to try the concepts while saving other PTs in pristine condition to get practice that is as close to the real thing as possible. Save the newer tests for full PTs while "cannibalizing" all the rest!