LSAT PrepTest 61 Logic Game Explanation #1

The October 2010 LSAT (PrepTest 61) Logic Games section seems to have given people enough trouble that it makes sense for me to publish complete explanations for each of the 4 Logic Games in the section.

Don't look at these explanations until you've taken PrepTest 61 as a full-length timed exam.

At the moment, I'm publishing these explanations primarily for those who want to review the exam they just took.

This LSAT Blog post covers the first Logic Game of the October 2010 LSAT.

Also see:

PrepTest 61 (October 2010 LSAT), Game 2 Explanation
PrepTest 61 (October 2010 LSAT), Game 3 Explanation
PrepTest 61 (October 2010 LSAT), Game 4 Explanation

Explanations for Recent LSAT Logic Games

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The workers here are Faith, Gus, Hannah, Juan, Kenneth, and Lisa, and they must be assigned to either car 1 or car 2. Each must have a driver as well.

This information, combined with the rules, gives us a very basic initial main diagram:










Explanation of basic initial main diagram:

This is what I call a "Grouping: Splitting" game because we are splitting (or dividing) the variables (in this case, workers) into exactly two groups, both of which are present. I represent each group vertically, rather than horizontally, because the game has no ordering component.

In this game, the 6 workers are being divided into two different cars. We know that each car has at least 2 people in it, so I've drawn 2 slots in each column. Each car has exactly one driver, so I've designated the top slot in each column as the "driver" slot by writing "(Dr)" to the side of that row.

I've also placed "(Dr)" to the sides of F/G and F/K, since one of each pair must be a driver.

On the other hand, G and L must be together, but it's not required that either one be a driver.

These rules have no bearing on which car is "car 1" and which car is "car 2" leading us to only 4 major possibilities based upon which people end up being the drivers.

Possibility #1:
We can have F drive H and have K drive J.

Possibility #2:
We can have G drive H and have K drive J.

Possibility #3:
We can have G drive H and have F drive J.

These 3 possibilities all assume that the two blocks involving H and J being passengers are separate. However, what if they were one and the same? This would lead us to:

Possibility #4:
We can have F drive both H and J in one of the cars. The other car would have to hold the GL block because each car must have at least two people. The GL block can't be in the same car as F, H, and J, because then we'd have 5 people in one of the cars and only one in the other.

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Note that none of these possibilities have any relationship to whether the workers are in car 1 or car 2. Car 1 and car 2 are completely interchangeable.

Here's what these 4 possibilities actually look like (click to enlarge):

In each of the possibilities, we can now fill in the remaining people.

In Possibility #1, all we have to do is keep G and L together, and this block can easily go on either side, so I've placed it "on the fence."

In Possibility #2, L must go in G's car since they must always be together. We've satisfied all conditions, so F is "on the fence."

In Possibility #3, L must go in G's car since they must always be together. We've satisfied all conditions, so K is "on the fence."

In Possibility #4, we've satisfied all conditions, so K is "on the fence."

Our diagram now looks like the following, and almost everything is determined:







Now, on to the questions:

Question 1:

Each of the incorrect choices will violate at least one rule.

Choice A happens to fit Possibility #4 and just jumped out at me, so I'd pick it and move on.

However, I'll explain why the others are invalid scenarios:

Choice B doesn't have J with either F or K. Eliminated.

Choice C doesn't have G and L together. Eliminated.

Choice D doesn't have H being driven by either F or G. Eliminated.

Choice E doesn't have J being driven by either F or K. Eliminated.


Question 2:

Choice A works in Possibility #3. Eliminated.

Choice B works in Possibility #1. Eliminated.

Choice C works in Possibility #4. Eliminated.

Choice D works in Possibility #2. Eliminated.

By elimination, Choice E is our answer, and we see that it doesn't occur in any of the possibilities.


Question 3:

If L is driving, we must be in Possibility #4. Since K's on the fence, it could easily be with F, and choice A is our answer.

The other choices can all be eliminated simply because none of the others can occur in Possibility #4.


Question 4:

F being with two other workers prevents Possibility #1 from being relevant to this question. F not being the driver prevents Possibilities #3 and #4 from being relevant to this question.

So, only Possibility #2 is relevant, and F goes to the car with K and J.

The hypothetical scenario drawn for this question should look something like the following:









(I've placed Car 2 on the left and Car 1 on the right simply to make it look more like the original possibility. You may want to draw a new diagram with the columns reversed if that feels more comfortable to you.)

In this diagram, the person in F's car besides the driver and F is J, so choice C is our answer.


Question 5:

This is a general question to which any of the possibilities might apply, so let's look at the general main diagram again:







Choice A can be satisfied in Possibility #4, so it's eliminated.

Choice B can be satisfied in Possibility #1, so it's eliminated.

Choice C can be satisfied in Possibility #1, Possibility #2, or Possibility #3, so it's eliminated.

Choice D can't be satisfied in any of the possibilities, so it's our answer. The cases in which K could be with only one other worker are when K himself is the driver.

I'll go through Choice E anyway for you:

Choice E can be satisfied in Possibility #4, so it's eliminated.

Photo by al7ayer