To cut costs, a high school modified its airconditioning system to

Question

To cut costs, a high school modified its airconditioning system to increase its efficiency. The modified system, however, caused the humidity in the school air to decrease by 18 percent. Twenty-four hours after the decrease in air humidity, a 25 percent increase in the number of visits to the school nurse was reported. This shows that a decrease in humidity can make people ill.

The argument depends on assuming which one of the following?

(A) At least some of the visits to the school nurse after the system was modified were due to illness.
(B) Most of the students at the high school suffered from the decrease in air humidity.
(C) It takes 24 hours after a person is infected with a virus for that person to exhibit symptoms.
(D) A decrease of 18 percent in air humidity causes an increase of 25 percent in one’s probability of becoming ill.
(E) Modifying the air-conditioning system proved to be an ineffective way to cut costs.

Source: LSAT

RMD007 · Accepted Answer

Premise - 18% decrease in humidity ----> 25% increase in nurse visits Conclusion - So humidity decrease---> MAKES ---> People ill Negate A - None of the visits to the school nurse after the system was modified were due to illness -- Conclusion shatters.... Need Kudos to unlock GmatClub tests..

himani2093 · Answer

The option says that the most students suffered from the humidity. If you want to quickly guess whether the option is right or wrong, simply scrutinise each and every word.

Here—>
It said that students suffered, now we dont know whether they suffered enough to go to doctor or what kind of suffering was there? It can be mild discomfort also. 
So that’s how we cannot be sure of this answer option.

Bunuel · Answer

EXPLANATION FROM Fox LSAT

How do we know there wasn’t a rampant gonorrhea outbreak among the students at Skank Unified High that same day? Or how do we know that the AC didn’t happen to get installed right before final exams, when everyone invents bogus illnesses and goes to the nurse? Or how do we know the school bus didn’t get in a 50-car pileup, causing massive injuries among the students and requiring nurse visits?

Yes, the humidity dropped. Yes, nurse visits increased. But we have no proof that one thing caused the other.  Correlation does not prove causation .

We’re asked to identify an assumption. I think it will be something that points out that  correlation doesn’t necessarily prove causation .

A) Well yeah. If this isn’t true, it becomes, “None of the visits to the school nurse after the AC system was modified were due to illness.” If that’s true, then how can it be true that the AC change  caused  illness? This must be true in order for the argument to make sense. Therefore it is a Necessary Assumption of the argument.

B) No, it’s not necessary that “most” students suffered in order for the argument to make sense. Even if “less than half” of the students got sick, the illness could still have been caused by the AC. So this isn’t necessary.

C) Who said anything at all about viruses? There is no way this was assumed by the speaker. Nobody is even talking about it. (There are all sorts of illnesses that have nothing to do with viruses.)

D) This strengthens the argument. But it’s so specific that there’s no way it’s a  necessary  support for the argument. What if a decrease of 18 percent in air humidity causes an increase of 2500 percent in one’s probability of getting ill? If that’s true, then D is false. But the argument would still make sense.  On a Necessary Assumption question, the opposite of the correct answer choice should kill the argument . That’s how you know something is necessary! Example: Oxygen is necessary, because without it you die. Food is also necessary. But pizza is not necessary, because without pizza you can still survive.

E) Costs are irrelevant.

Our answer is A.

rakeshtewatia0105 · Answer

can anyone please explain why "b" is not the correct answrer?

Abhishek009 · Answer

Most = > 51%

Now, the stimulus states that only 25 % went to the nurse.... What about the others ? Thus this assumption doesnt hold good.

lakshya14 · Answer

I doubt (A) being the correct answer, it only says at least some. Had this been the inference questions this would be correct.

CrackverbalGMAT · Answer

Hi Lakshya

Let us analyse the conclusion and the premises on which it is based:

Conclusion:  A decrease in humidity can make people ill.

Premise:  Twenty-four hours after the decrease in air humidity, a 25 percent increase in the number of visits to the school nurse was reported.

If you notice, there is a subtle language shift between the premise and the conclusion. The premise talks about visits to the nurse and the conclusion talks about making people ill. The underlying assumption, therefore, has to be that the two are connected. Option (A) states exactly this.

Alternatively, you could try to negate option (A).

Negated (A): None of the visits to the school nurse after the system was modified were due to illness.

If none of the visits were due to illness, then the 25% increase was also not due to illness. This negates the conclusion that decrease in humidity makes people ill (based on the premise of increased nurse visits), since none of the visits were due to illness.

Hope this helps.

VerbalBot · Answer

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To cut costs, a high school modified its airconditioning system to

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