This is an explanation of the first logic game from Section III of LSAT Preptest 62, the December 2010 LSAT.
A motel operator is starting up services at a new motel. The operator is setting appointments for six services: gas, landscaping, power, satellite, telephone, and water (G, L, P, S, T, W). The rules determine the possible schedules of the service appointments.
This is, at first glance, a linear game where you just list the rules and apply them. But by drawing the rules on the diagram and making a couple of deductions, you can figure many things out up front.
First, let’s draw rules one and two. Water is before landscaping, and power is before gas and satellite:
Next, draw rules three and four directly on the diagram. Gas, satellite and telephone can’t go second or third, and telephone can’t go sixth:
Many people stop here. But with so many restrictions, we should see if there are other restrictions we can add to the diagram.
For instance, gas and satellite can’t go first (rule 2). Since there are so many gas/satellite restrictions, you should draw that on the diagram:
Next, let’s see who can’t go last, since it also has a restriction. Power can’t, because power is before gas/satellite. And water can’t, because water is before landscaping:
TWP can’t go last….so only gas, satellite and landscaping can go last. This is an important deduction! And gas/satellite must take up two of the last three spaces.
I’d like to have a better sense of who can go where. If you just think about a deduction but don’t write it down, it’s easy to forget.
I divided the diagram into two. Gas and satellite are always 4-6. Water is always 1-3, because it’s before landscaping. G/S already take up two of the three final spaces, so there’s no room for G, S and W – L:
This way, it’s easy to see who must go 1-3 and who must go 4-6.
(Note: Landscaping doesn’t have to go 4-6. You just can’t put water 4-6, because landscaping is after water.)
Now we’re set. You do need to remember the first two rules to use this diagram properly, of course.
Note that I only drew the final diagram as my main diagram. For individual questions, I drew this diagram:
It has no detail. I look down to the main diagram to see detail and fill in the local diagrams. I keep my main diagram near the questions so I can easily look down at it.
In these explanations, I include details on all the local diagrams, for clarity. But my local diagrams are rather more minimal.
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