This is an explanation of the first logic game from Section II of LSAT Preptest 74, the December 2014 LSAT.
A six-member band held a concert. The band consists of a guitarist, a keyboardist, a percussionist, a saxophonist, a trumpeter, and a violinist (G, K, P, S, T, V). Each of them performs exactly one solo. You must use the rules to determine the possible sequences of the solos.
This is a pure sequencing game. This type of game has been changing on modern LSATs.
If you look at older LSATs, say, earlier than PT 40, you’ll see that sequencing games were very, very, standardized. Do one and you could do all of them easily.
This worked in the early days, because not that many people prepped for the LSAT. Standard sequencing games were hard if you had never seen them before.
But since they were the most learnable logic game, students who prepped started doing really, really well on sequencing games. It was an unfair advantage.
So the LSAC began throwing twists into sequencing games. The underlying logic was the same, but the games became more complex.
This game continues that trend. It introduces dual scenarios into a sequencing game, which I’ve never seen before. Study this game well, and repeat it a few times. I expect this game will become one of the standard types on future sequencing games.
We’ll start with the basic setup. Here’s the diagram, plus the 1st rule (the guitarist doesn’t perform fourth):
Next, rule 2 says that the percussionist is before the keyboard player:
The third rule also mentions the keyboard player, so it can be combined with the first rule. It’s very useful to combine sequencing rules:
This diagram lets us see, for example, that the percussionist performs before the guitarist.
The final rule is the most complicated rule of the game. First, you must think about the full implications of the rule. It says that the saxophonist is after the trumpeter, or the percussionist, but not both.
The saxophonist can only be before one of the trumpeter or the percussionist. So if the saxophonist is after the percussionist, then the saxophonist is before the trumpeter. And vice versa:
The reverse is also possible. Effectively, the saxophonist has to be between the percussionist and the trumpeter.
You could stop here, but there’s more to deduce. For instance, look what happens if you combine T–S–P with rules 2 and 3:
If T–S–P are in that order, we know almost everything. The only uncertainty is where V goes. It could go anywhere earlier than K, including first.
What about P–S–T? We can draw a combined diagram there as well:
We’re still not done. You always must consider restricted variables. G is very restricted. Let’s see what we know about G:
- G can’t be fourth.
- G has to be after P, K and V
We can combine those to say that G can’t be in the first four spaces. So P, K, V and at least one other band member must be before G. In the diagram above, that means S must be before G:
So we have two scenarios. They depend on whether the order is P–S–T or T–S–P:
Scenario 1 (T–S–P)
Scenario 2 (P–S–T)
These diagrams make solving the game lightning fast. If a question asks what “could be true”, you can just check if an answer is possible in either diagram.
Note that you should draw both of these diagrams on the second page, under the questions. That way, it’s faster to refer to the diagrams when solving questions.
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