This is an explanation of the third logic game from Section II of LSAT preptest 71, the December 2013 LSAT.
Six books will be discussed in a six-week literature course (F, K, N, O, R, T). You must arrange the books in sequence and determine whether they will be summarized.
This is a linear/sequencing game, with a second element: the courses are either summarized or not summarized.
I don’t have any special approach for this type of game. I just mark summarized or not summarized under the diagram. Keep it simple.
(There will be examples summarized/not summarized diagram on the questions)
At first I thought this was just a sequencing game. I drew rules 3 and 4. Here’s rule 4:
I then added rule 3:
Most people would stop there. In fact, I did stop there on my own setup. But when I got to question 14, I noticed that this game is very restricted. Look at O. O is stuck in the middle. FTN are always before O, and KR are always after O.
So O is always fourth! This deduction makes the game much simpler. I redrew the sequencing rules as this diagram:
When I want to show semi-certain placement in a linear diagram, I draw some variables floating above the diagram. For instance, KR are always to the right of O. So I drew them in that position. The comma indicates that they are reversible.
I’ve done the same thing with “ F, N – T ”. N is always before T, but the comma indicates that F could be before them, after them or in the middle.
Drawing the diagram this way may seem like a small change. You might think “I could have figured all that out without the diagram!”. But did you?
In any case, all logic games diagrams are just a tool to do things faster. This particular diagram let me fly through this game in six minutes. As much as possible, you should take knowledge out of your head, and put it on the page in the clearest possible form. You want to always know that O is fourth, without thinking about it.
There are two more rules. Courses can’t go together if they’re summarized. I drew it like this:
That’s more of a reminder than anything else. I kept that rule in my head. Remembering it will help you go fast. You should always take 10-20 seconds at the start of a game to make sure you’ve memorized the rules.
The second rule says that if N is not summarized, then T and R are both summarized:
I only drew that. I’ve done enough logic games that the contrapositive is obvious to me. However, if it takes you time to see the contrapositive, then you should draw the contrapositive as well:
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