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#22 - The airport's runways are too close

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Complete Question Explanation

Must Be True. The correct answer choice is (D)

In bad weather (when visibility is poor), the airport cannot land planes on adjacent runways at the
same time, because the runways are too close to one another. This reduces the maximum number of
planes that the airport can land each hour, from 60 in good weather, to 30 in bad weather. Schedules
assume good weather, the author provides, so bad weather causes big delays.

    Premise: Bad weather reduces the maximum number of planes per hour, from 60 to 30.

    Premise: Airline schedules assume good weather.

    Conclusion: Bad weather causes major delays.
What has the author told us (although not explicitly) about the number of planes scheduled to land at
the airport? Bad weather, as we know, can cause major delays; reducing the number of planes that
can land, from 60 to 30, causes these delays, so it must be that 30 planes per hour is not enough to
keep things at this airport running smoothly.
The question that follows is a Must Be True question, so the correct answer choice must pass the
Fact Test: Only the right answer choice will be able to be confirmed by the information provided in
the stimulus.

Answer choice (A): This answer choice claims that each runway can only land half as many planes
in bad weather as in good. Based on the information provided in the stimulus, the issue with bad
weather is that only one of two runways can be used in poor visibility—that is why bad weather
leads to delays. This clever wrong answer caught many test takers, because the stimulus provides
that the number of planes that can possibly land on the two runways together is cut in half, but that
does not necessarily mean that the capacity of each individual runway is cut in half. This choice
cannot be confirmed by the stimulus, so it cannot be the correct answer choice.

Answer choice (B): The stimulus provides that good weather allows for adjacent runways to be used
simultaneously, but that does not dictate that planes are landing constantly on both. Since this choice
is not confirmed by the information in the stimulus, it fails the Fact Test and should be ruled out of

Answer choice (C): This choice claims that serious delays result from simultaneous use of two
runways—but according to the stimulus, the delays come about when planes are unable to land
simultaneously. Thus, this choice is something of an Opposite answer.

Answer choice (D): This is the correct answer choice. If, as the author of the stimulus provides,
the 30 plane per hour limitation is too much, and thus leads to delays, it must be that more than 30
planes per hour are normally scheduled.

Answer choice (E): The information provided by the author is limited to what happens in bad
weather (major delays). Since no information is provided regarding the airport’s normal operations,
this choice cannot be confirmed by the information in the stimulus, fails the Fact Test, and should be
ruled out of contention.
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So, the stimulus says that the airport allows only 30 planes an hour to land in poor weather; in good weather 60 planes are allowed to land. Hence, I chose, ans. choice A. So, why is ans choice D correct?

The only thing that i think makes A wrong is that that the stimulus doesn't specify that 30 planes are landing, an hr, on each runaway in poor weather. I maybe wrong here but just my thoughts.

- Arindom
Nikki Siclunov
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Hi Arindom,

Thanks for your question. Answer choice (A) is attractive, but we can't prove it to such exactitude. We know that in poor weather, the overall airport capacity is reduced by half; however, we cannot conclude from this that the capacity of each runway is reduced by half. This is an Error of Division, assuming that a property of the whole class is also applicable to each individual member of that class. It's entirely possible that the capacity of Runway A is reduced by 70%, the capacity of Runway B is reduced by 50%, and the capacity of runway C is reduced by 30%.

Hope this clears things up!
Nikki Siclunov
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I got this right but was confused on A, and even looking at multiple explanations online I don't get what A is saying and why its wrong... can someone please help :cry:
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I’m a bit confused about how one recognizes that 30 planes is too many in the stimulus? I understood it as the delays happen because the schedule is done thinking the weather is nice and then when it’s not, they have to delay planes landing simultaneously to accommodate. What am I missing?

Thank you!
Malila Robinson
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Hi Akanshalsat,
Answer A is attempting to distract you with numbers. The 2 numbers we are given in the stimulus are 60 (good weather) and 30 (bad weather). Answer A describes half as many planes doing something in bad weather as they are able to do in good weather. That part of the answer is fine, 30 is half of 60. The problem comes from the specificity that Answer A gets into when it says: "...allowed to land each hour on any one runway...". Since this is a Must Be True question we need the answer choice to restate something from the argument. But nothing in the argument specifies how many planes will land on a single runway, it just states how many will land at the airport in general over the course of an hour. Answer A brings in too much outside info, so it is incorrect.
Hope that helps!
Malila Robinson
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Hi Marina7,
Your interpretation is correct, and comes largely from the last sentence in the stimulus. Where did you see that 30 planes was too many?
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Hi can someone explain ac D in a different way. I am confused as how it is described above. Its not making too much sense to me, thanks.
Brook Miscoski
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The stimulus tells us that you can land 60 pph in good weather, but only 30 pph in bad weather. It then tells us that airlines assume good weather, which causes delays during bad weather.

The easiest way to think about this is to realize that airlines assume that 60 pph is the max (they plan for good weather). Looking at the choices:

(A) There's no evidence for the exact proportion.
(B) We don't know that simultaneous use means that.
(C) This is contrary to the stimulus.
(D) Yes, 60 is more than 30--right answer.
(E) No information about delays in good weather.

So there you have it--D stands out. Maybe the airlines don't plan for all 60 flights, but they're planning for more than 30, which is why bad weather causes delays.