This is an explanation of the second logic game from Section II of LSAT Preptest 63, the June 2011 LSAT.
Six skydivers – Larue, Ohba, Pei, Treviño, Weiss, and Zacny (L, O, P, T, W, Z) will dive from a plane one at a time. The entire skydiving team will dive. You must use the rules to determine the possible orders they can dive in.
This is an interesting game. You could solve it effectively by making a list of rules and applying them to every question. But you can solve it even faster by making two main scenarios.
Let’s look at the fourth rule first. It’s the most complicated. Pei is after one of Obha or Larue, but not after both.
The LSAC has been including this type of rule more and more on modern sequencing games. It’s confusing the first time you read it. What this rule is really saying is that Pei is in the middle of Obha and Larua, in either order. Like this:
Now, Larue was mentioned in the second rule as well. Anytime a game mentions a variable in two rules, there’s usually a way to combine those rules.
Use the second rule to make two scenarios
First, let’s draw the second rule. There are two possibilities: Larue goes first or last. Whenever there are only two possibilities, you should split the diagram:
How do we combine the rules? Look at both diagrams. The placement of Larue determines the order for Pei and Ohba in each scenario. If Larue is first, then we get P – O. If Larue is last, then we get O – P.
I’ve drawn P – O and O – P floating above the diagram. This is a reminder of what order the members must be in, in each diagram. There’s no sense making a deduction then not drawing it. This way you can never forget the order of L, P and O in each scenario.
We can get separate deductions in each scenario
Next, let’s add the third rule. Weiss and Zacny can’t be last. This only affects the first scenario, since L is last in the second scenario:
Finally, Treviño is before Weiss. That’s just a simple ordering rule, drawn like this:
However, I prefer to place that rule directly on the diagram, along with the remaining variables. When you see everything together, you can make deductions and form scenarios:
Now we can see everything at once. The commas indicate there’s no ordering rule. So in the second diagram, Zacny could go first, second, third…. anywhere but last.
These two scenarios let you visualize all the possibilities without getting sucked into drawing endless “could be true” scenarios.
But we’re not done. Notice that the first scenario is more restricted than the second scenario. Weiss and Zacny can’t go last. Whenever a space has restrictions, you should see who can go there.
- Not Weiss and Zacny, due to the third rule.
- Not Treviño, because Weiss is after Treviño.
- Not Pei, because Obha is after Pei.
- Not Larue, because Larue is first in scenario one.
The final scenarios are very restricted
Only Obha can go last in scenario 1!
This is the final diagram I used to solve this game. I had never seen this game before, and I did it in five and a half minutes. Such a diagram is far faster than the normal approach of making a list of rules and applying them.
(On some games I do make a list of rules and apply them, because it’s not possible to make a diagram like this.)
I recommend you print a fresh copy of this game, and draw this diagram on the page. Then solve the questions. Do this before you look at the explanations. I want you to practice visualizing scenarios using this kind of diagram.
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