March 23, 2016 at 8:05 am #1617jaydParticipant
So, I’ve reviewed this game several times and can complete the game using my memory from 7Sage/LSAT Blog.
I am really struggling to understand one of the key inferences from the game, however.
~R –> J –> ~M
In this chain, we supposedly have an “either/or” rule with ~R –> J and then a “not both” rule with J –> ~M.
I know this is a key inference in the game, and is supposedly easy to spot if you have everything chained up correctly. I have everything chained correctly and cannot wrap my head around how one can just quickly infer these rules.
Can somebody please break this down for me and possibly recommend some drills/things to think about that could help?
Thanks again! Words cannot express how thankful I am for this forum!
March 23, 2016 at 10:45 am #1618LSAT DanParticipant
When you translate conditional rules in a logic game, always add the contrapositive to your checklist. The first rule is:
~R –> J
The second rule is:
M –> ~J
But if you take the contrapositive of the second rule, it’s:
J –> ~M
Now you have J in the same state (not-negated) as the necessary term in one rule (~R –> J) and the sufficient term in another (J –> ~M). So the connection (~R –> J –> ~M) is direct. The essence of combined rules is being able to use the same term as the sufficient term in one rule and the necessary in another. Writing out the contrapositive of all of your rules maximizes the chances that you’ll be able to do that. It basically provides more possible triggers. Assuming that you correctly untangled the rules and diagrammed them correctly, that’s pretty much all it comes down to.
Personally, I don’t consider this a key inference. I find that for most students, combining conditional rules (particularly in in-&-out games) adds more confusion and takes more time than it’s worth. I think that a concise, accurate checklist of individual rules (and their contrapostives) is the better way to go. However, I’m certainly in the minority among LSAT tutors/writers with that view. On the other hand, I *do* believe that combining rules in sequencing games is very helpful, because of the additional visual cues (stuff on the left happened before stuff on the right) that it provides. Just my 2 cents.
March 23, 2016 at 4:03 pm #1621LSAT DanParticipant
🙂 It happens…sometimes it’s hard to see what’s right in front of your face, especially if you’ve been hitting it hard for a while. Taking a step back when you need to is never a bad idea. Just remember that inferences generally come from multiple rules affecting the same variables. If you keep that idea in mind, it will help focus your attention where it needs to be.
March 29, 2016 at 12:47 pm #1632ndoria25Participant
I was also just working on this game and hope you can lend some assistance. Obviously, the game hinges on conditional rules and one slip up notating can get you in big trouble. I am positive I notated the rules correctly, but for some reason, I CAN NOT see why the answer to #15 is D. I must have done and redone this question a dozen times and I am still not getting it. Like JD, I have been prepping hard and fatigue might be getting the best of me as I am sure the answer is quite obvious. Any help would be greatly appreciated!
March 29, 2016 at 6:09 pm #1636dannypearlbergParticipant
According to question #15, Alice takes Statistics at 3pm and Geography.
If she takes Statistics at 3pm, she does not take statistics at 9am (according to the setup, “no one is allowed to take any course more than once per semester”).
If she does not take statistics at 9am, then she does not take psychology (this is the contrapositive of the fourth rule).
If she takes Geography, then according to the last rule she does not take World History.
At this point, there are three courses that she isn’t taking: Statistics at 9am, World History, and Psychology. Since she takes four courses, there are only four available spots for courses that she doesn’t take, so now there is only one spot left. Combining the first two rules shows that if she doesn’t take Russian then she takes Japanese, and if she takes Japanese then she doesn’t take Macroeconomics. Thus, if she doesn’t take Russian, then she also doesn’t take Macroeconomics.
Since there is only one spot left for a course that Alice doesn’t take, it can’t be the case that she doesn’t take Russian, because if she doesn’t take Russian then she also doesn’t take Macroeconomics, which means that there would be five courses that she isn’t taking. But that’s one course too many. So she must take Russian.
Hope that helps 🙂
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