#5 - Local, Justify

[Administrator]

Complete Question Explanation
(The complete setup for this game can be found here: lsat/viewtopic.php?t=4778)

The correct answer choice is (C)

Justify questions, which appear infrequently in the Logic Games section, require you to select an answer choice that, when added to the initial rules of the game, forces the condition requested in the question stem to occur. In this case, the answer choice must force R to be a journalism major. Recall that R speaks on liberty (fourth rule) and majors in either history or journalism (fifth rule). For R to major in journalism, we need to ensure that someone else is a history major who speaks on liberty.

Answer choice (A) is incorrect. Just because M is a geology major and P is a history major does not mean that R is a journalism major: it is also possible that O is a journalism major.

oct12_game_1_#5_diagram_1.png

Answer choice (B) is also incorrect. If O is a geology major, then M must be a history major: otherwise we would have three geology majors (N, O, and M). Since one of the two conditions in this answer choice necessitates the other, we can conclude that the second condition does not add a unique point of restriction to the game. To the observant test-taker this should be a red flag, as the correct answer choice is likely to introduce two independent points of restriction in order to force the condition requested in the question stem to occur. And indeed, a quick set-up reveals that if O is a geology major, R need not be a journalism major:

oct12_game_1_#5_diagram_2.png

Answer choice (C) is the correct answer choice. As discussed above, if O is a geology major, then M must be a history major. If we also know that P is a history major, we’d have sufficient information to determine the two history majors (M, P) and the two geology majors (N, O). Clearly, then, the remaining variable R must be a journalism major in order to conform to the 2-2-1 distribution of history, geology, and journalism majors, respectively:

oct12_game_1_#5_diagram_3.png

Answer choice (D) is incorrect. The fact that M and N speak on friendship only helps establish the topic on which each student delivers a speech, not their respective majors. Furthermore, note that one of the two conditions in this answer choice is redundant, as we already know that M speaks on friendship from the third rule in the game:

oct12_game_1_#5_diagram_4.png

Answer choice (E) is incorrect for the same reason as answer choice (D) is. The fact that M and P both speak on friendship only helps establish the topic on which each student delivers a speech, not their respective majors. And, as with answer choice (D), one of the two conditions in this answer choice is redundant, because we already know that M speaks on friendship from the third rule in the game. This should be a red flag, as the correct answer choice is likely to introduce as many independent points of restriction as possible in order to force the condition requested in the question stem to occur:

oct12_game_1_#5_diagram_5.png

This question also provides an excellent example of the technique of using hypotheticals from other questions to eliminate incorrect answer choices. Since answer choices (D) and (E) both include a condition we know to be true from the third rule of the game, each of them entails a single point of restriction that has already been examined in prior questions. For instance, answer choice (D) states that N speaks on friendship. From question #4 we know that this scenario leaves open the possibility that R majors in history, which would conflict with the desired result of question #5. Answer choice (E) can be eliminated by the same process: if P speaks on friendship, we know from question #2 that R can major in either history or journalism.

Finally, when solving Justify questions, look for answer choices that introduce as many unique and independent points of restriction as possible, so as to increase the probability that the condition requested in the question stem is forced to occur. Here, each of the five answer choices ostensibly introduced two additional conditions to the game, but only in answer choices (A) and (C) were these conditions independent and unique. In answer choice (B), one of the conditions logically required the other, whereas in answer choices (D) and (E) one of the conditions was a given. While you should not eliminate an answer choice simply because it contains a restatement of an original rule, you should certainly approach such an answer choice with a great deal of suspicion.

[martinbeslu]

I think my diagrams are throwing me off. I saw that there were two students that had only two options for their majors. P's major was H/J and R's major was H/J and I jumped to the assumption that if P was a history major then R must be a journalism major. After looking at the explanation I totally understand that both P and R could be history majors, but when we have diagrams that look like this many times selecting one of the two option variables in one position forces the selection of the other two option variable in the other position.

Do you have any suggestions on how to notate that there is no need for R to be a J major just because P is an H major? Any suggestions to help keep this organized in my mind when quickly going through the problems?

[Adam Tyson]

It's a small thing, martin, but I do have a suggestion, and it has to do with the slashes. If I want to show that when P is H, then R must be J, I would do it by putting "H/J" above P and "J/H" above R. Notice how the order of H and J swapped? In my mind, that tells me that whatever is to the left of each slash goes together and whatever is to the right of the slash goes together. That is, if P is H (which is to the left of the slash over my P), then R is J (because that is also to the left of the slash). When that is NOT the case - where they can both be H, as here - then I do NOT reverse the order, and instead show them both as "H/J". When I see that, I make no assumptions about the lefts and rights going together. That small difference is my shorthand.

Another approach is simply to not put the split option about those variables, if doing so leads to the incorrect inference that you made. Instead, simply put the not laws for G under each variable and leave the space above them blank. Your variable list, with two Gs and two Hs and one J will be enough to help you with the specific local questions when they come up.

Ultimately, it's up to you to choose the method that is most efficient and least confusing for you. We like our method, but we know that it is not the only way to accomplish things, and every student has to be comfortable with the tools they choose to use. If my suggestions don't work for you, try another, and another, until you find one that makes sense to you.

Good luck!

[mandrewg]

I was curious if there is a preferred approach to this question, I.e. should I just start plugging in the answers into several diagrams or is there a more efficient approach? I couldn't delineate the process from the explanation above and any insight would be helpful (just started my online class and took the pretest and reviewing answers now, so thank you in advance! I'm probably missing some fundamentals most likely....).

[Paul Marsh]

Hi mandrewg! Great question. Let's walk through how to think through this one.

Check out the first couple paragraphs at the link below; it's a well-written explanation on how to approach a similar question:

https://forum.powerscore.com/lsat/viewtopic.php?t=15500

Basically, for Justify questions like this we don't want to just dive into the answer choices and try them one by one. It takes way too long. Instead, before looking at the answer choices, we want to take a minute to Pre-Phrase the conditions that would be powerful enough to bring about the result that the question is looking for (here, that's Rana being a journalism major - or in shorthand, R is J).

So just looking at our master diagram and inferences, what would allow us to know that R is J? Well, we know from our diagram that R is limited to being H or J. So it seems like the easiest way to know that R is J is to rule out the possibility that
is H. We know that there are only 2 H majors - one H is giving a lecture on F, the second H is giving a lecture on L. We also know that R is giving a lecture on L. So if we can pin down where both of the H's are (or at least where the H giving the lecture on L is), then that will allow us to infer that R is a J major. Since P (like R) can be either H or J, we are probably going to want to pin one of the H's on P.

So as we come down to the answer choices, we are not just trying out each answer choice in order. Instead, we are aggressively looking for which answer choice will tell us where both H's are. Just from glancing at (D) and (E), we can guess that those won't be much help. We turn to (A), (B), and (C). Since (as mentioned earlier) we want to pin one of the H's on P, we focus on (A) and (C) especially. Might as well start with (A).

If M is G, does that tell me where the second H is? Nope, could be O or R. Quickly move on to (C).

What about if O is G, does that tell me where the second H is? Yes - since O is G and N is G and there are only two G majors, that means M has to be H. Since we know that M and P are both H majors, that means R has to be a J major. (C) is our right answer.

To sum up - the best method for attacking these Justify Logic Game questions is to take a minute to Pre-Phrase the conditions that be powerful enough to bring about the result the question is looking for, and then look for the answer choice that provides those conditions. Hope that helps!