LSAT 155 - Section 1 - Question 21

The question stem says the reasoning in which one of the following is most strongly supported by the guidelines. This is a rarer type of question though we have seen it plenty before. It’s like MSS in that the support flows down from the stimulus into the answers. They're asking us to take the guidelines in the stimulus and push them into the arguments in the answers to improve their reasoning. But that’s like a PSA question. Instead of the stimulus containing an argument searching for a conditional in the answer, it's the other way around. The stimulus contains a conditional searching for an argument. This is a cosmetic difference.

The stimulus gives us a ton of rules in conditional form. The first one is that if a radiant floor cooling system is to be installed or if it is to be a luxury hotel, then a radiant floor heating system must be installed. The sufficient condition here is a disjunctive, it's "or." That means we can split the arrow, so to speak. A radiant floor cooling system and a luxury hotel are each independently sufficient to demand the installation of radiant floor heating.

rf-cool → rf-heat

luxury → rf-heat

The next sentence is the only other conditional. It hooks up to radiant floor cooling. It says a radiant floor cooling system should not be installed in any hotel that is located in a region that tends to have high humidity during the summer. That means a necessary condition of installing radiant floor cooling is not high summer humidity. Or, contrapositively, if we’re in a hotel located in a region that tends to have high summer humidity, then no radiant floor cooling.

rf-cool → /region-high-sum-hum

Before looking at the answers, take stock of what conclusions are reachable. In general, we can run conditionals forward or contrapose backwards. Running them forward reaches the necessary conditions. Contraposing them backwards reaches the failure of the sufficient conditions. For these conditionals, that means there are four reachable conclusions:

rf-heat (either satisfying rf-cool or luxury)

/region-high-sum-hum (satisfying rf-cool)

/rf-cool (either failing rf-heat or failing /region-high-sum-hum)

/luxury (failing rf-heat)

It’s also important to take note of what conclusions are unreachable. That will help us quickly eliminate answers that are wrong on the basis of their logic alone. In general, affirmation of the necessary condition and the failure of the sufficient conditions are unreachable. Here, that means conclusions of rf-cool or /rf-heat are unreachable.

The first pair of answers I want to consider is Answer Choice (D) and Answer Choice (E). They both contain unreachable conclusions and hence are both wrong on the basis of their logic alone. Look at the conclusions in each. (D) concludes that the newest Bonjour hotel should have neither radiant floor heating nor radiant floor cooling. The “/rf-heat” portion of the conclusion is unreachable. (E) concludes just the opposite, that it should have both. The “rf-cool” portion of the conclusion is unreachable.

The conditionals in the stimulus cannot possibly be used to arrive at those conclusions. We were not told the necessary conditions of having radiant floor heating. And because we weren't told those necessary conditions, we don't know what to fail in order to draw the conclusion that there should be no radiant floor heating. This is the same logic with regard to radiant floor cooling. We need to know what its sufficient conditions are. But the stimulus doesn't tell us what the sufficient conditions of having radiant floor cooling are. Therefore we don't know what we need to satisfy to trigger radiant floor cooling.

Now contrast with Correct Answer Choice (B). It concludes that the newest Bonjour hotel should have radiant floor heating but not radiant floor cooling, rf-heat and /rf-cool. Those are reachable conclusions. (B) says that the region has high humidity year-round. That means it has high humidity during the summer. That fails a necessary condition of rf-cool. (B) also says that the hotel will be luxury. That satisfies one of the sufficient conditions for rf-heat.

Answer Choice (A) and Answer Choice (C) don’t suffer from logic issues like (D) and (E). They both contain reachable conclusions: /rf-cool. We can reach that conclusion in two ways, either failing rf-heat or failing /region-high-sum-hum, meaning either saying that the hotel won’t have radiant floor heating or saying that the hotel will be in a region with high summer humidity. But (A) and (C) don’t do either.

(A) says it’s not newly constructed. That immediately kicks it out of the domain of the stimulus which is guidelines for newly constructed hotels.

(A) and (C) both say that they are not luxury, but that doesn’t trigger anything.

(C) also says the newest Bonjour hotel will have radiant floor heating. That also triggers nothing.