#18 - Until 1985 all commercial airlines completely

[brittany1990]

Hi!

After reading the stimulus and question stem, I identified it as a MBT. I prephrased that people who fly now are more likely to get airborne illnesses. I eliminated A,C, and D so I was left with B and E. I picked B since it matched my pre phrase but E is correct.

May you please explain why?

Thanks!
Brittany

[Nikki Siclunov]

Just because replenishing the cabin air less often makes it easier for airborne illnesses to be spread, that doesn't mean that people flying today are more likely to contract such illnesses. First off, there are a number of factors we need to consider before estimating the comparative likelihood of contracting an illness (e.g. number of passengers flying, virulence of the pathogen to be contracted, etc.). Even more importantly, the argument concerns commercial flights only, whereas (B) contains a generalization ("people who fly today"). When you consider the total number of passengers flying on private jets, military planes, helicopters, etc., it is possible that the overall likelihood of contracting an illness has not increased.

(E) avoids this problem by stating a claim that can easily be proven by referring to the last sentence of the stimulus.

[sarae]

why is answer choice B incorrect?

[Ron Gore]

Thanks for the question, Sara!

This is a Must Be True question. As always, the correct answer will be either a restatement of one of the facts or an inference permissible from a combination of facts.

In this stimulus, an inference is possible from combining some of the facts given. We know that until 1985 all commercial airlines completely replenished their cabin air once every thirty minutes. And since 1985, the replenishment interval has been changed to once every hour. We also know from the stimulus that the less frequently the cabin air is replenished in a plane in flight: (1) the higher the level of carbon dioxide in the plane, and (2) the easier it is for airborne illnesses to be spread.

So, combining the first two sentences of the stimulus with the last sentence, we can infer that since 1985, and because of the change to the interval at which the cabin air is replenished, the level of carbon dioxide in the planes is higher than it was prior to 1985, other things being equal, and that it is easier for airborne illnesses to spread now in the airplane cabins than it was before 1985, all things being equal.

The proper Prephrase is that the correct answer will ask about a restatement of any of these facts or the inference were able to infer from them.

Answer choice (E) is correct because carbon dioxide in the cabin air on a two hour commercial airline flight was lower than it is today on a similar flight. This inference is permissible because of the first fact, that due to the longer period between replenishment, the level of CO2 would be higher.

Answer choice (B) is an attractive incorrect answer because it could be true based on the second fact, that it is easier for airborne illnesses to spread. However, to infer that because it is easier for an illness to be spread on a plane that there is an increased probability that people who fly today are likely to, in fact, contract an airborne illness is an unsupported exaggeration of the facts that requires new information (e.g., that an airborne illness is actually introduced to the plane to be spread).

Hope this helps.

Ron

[PresidentLSAT]

Just came here to tell my fellow LSATers that if you are reviewing this question in 2020/2022, you should know that covid_19 is sufficient to make B wrong.

[lmrlmr]

Still a bit confused about how answer choice E is correct.

I was thinking that because we don't know how many people are on this two-hour flight, then how do we know that the level of CO2 is lower in 1980?
For example, what if there were 1000 people on a 2 hour flight in 1980 with the air being replenished every 30 minutes while in 1986 there are just 2 pilots, 2 flight attendants, and 1 passenger? I would think that the level of CO2 in 1986 would be lower.

Also, now that I've written that out, wouldn't the levels of CO2 be completely back to "zero" once they've replenished all of the air so ultimately after two hours they actually would be the same, i.e., "zero" units of CO2?

take off = 0 / 30 mins = 0 / 1 hour = 0 / 1.5 hr = 0 / 2 hr = 0
take off = 0 / 1 hour = 0 / 2 hour = 0

I'm saying "zero" because obviously it's not really possible for there to be zero units of CO2, but if they completely replenish the air then, isn't that what they're kind of saying?

Thank you!

[Rachael Wilkenfeld]

Hi lmr,

You are making many many assumptions here that are not supported by facts in the stimulus. Our stimulus does not say that replenishing air gets it down to zero at any point. The air in the plane doesn't sucked out all at once and replaced all at once. It's likely a slow process of replacing the air bit by bit over the course of the 30 minutes or 60 minutes. But, we certainly don't know we have a full cancellation of CO2 at any point in the flight.

The number of people on the plane in the flight from 1980 and from today would be similar if they were "similar flights" as answer choice (E) describes.

We don't want to add any assumptions to the facts given. Just by the facts, the less frequently the air is replenished in flight, the higher the CO2, and the easier it is for illness to spread. In 1980 air was replenished every 30 minutes. Now it's every hour. Doing something every hour is less frequent than every 30 minutes. So we can determine that the every hour plane has higher CO2, and is easier for illness to spread.

Hope that helps!

[lsattesttaker93]

Isn't E just too strong of a statement to make? Or is this supported because of the last sentence where it is relative: "The less frequently cabin air is replenished in a plane in flight, the higher the level of carbon dioxide in that plane and the easier it is for airborne illnesses to be spread."?

In addition to the strength of the answer I also felt confused with the fact that between 1980 and today, why couldn't planes have evolved technologically to still maintain the level of carbon dioxide pre-1985, but at a lower air replenishment rate?

The first thing I thought about was changing pool water:

Until 1980s all commercial pools replenished their water once every two days. Since then, all commercial pools have replenished their water once every week. The less frequently water is replenished, the higher the level of bacteria, and the easier it is to get waterborne illnesses to spread.

And obviously, we can say, there now exists powerful pool disinfectants, that didn't exist in the 1980s, which allow you to maintain the bacteria at normal levels without the frequency of water changes.

This seemed pretty common sense to me, and I felt like AC E was too definitive of a statement to make that didn't really address this. The "similar" in the last sentence feels like it protects the answer choice around questions about the flight itself (i.e. the density of the cabin, make-up of passengers, etc.)

[Luke Haqq]

Hi lsattesttaker93!

I'd be happy to answer the questions about answer choice (E).

Isn't E just too strong of a statement to make? Or is this supported because of the last sentence where it is relative: "The less frequently cabin air is replenished in a plane in flight, the higher the level of carbon dioxide in that plane and the easier it is for airborne illnesses to be spread."?

Yes, answer choice (E) is supported by that last sentence, and it isn't too strong of a statement. The stimulus gives us conditional reasoning:

LFRR More CO2

A less frequent replenish rate implies more CO2. In addition, we're given the sufficient condition in this conditional reasoning--"Since then the rate has been once every hour." Given that the preceding sentence mentions that the rate had been every 30 minutes, we know that this once-every-hour rate is a less frequent replenish rate. In other words, we have LFRR and the above conditional reasoning reflects that if we have LFRR we can infer More CO2.

This is what answer choice (E) reflects: "In 1980 the level of carbon dioxide in the cabin air on a two-hour commercial airline flight was lower than it is today on a similar flight." Today we have LFRR, which implies More CO2.

We don't know other things like whether or not technologies have evolved and bringing them in is unnecessary and can detract from the correct answer. One might also speculate--what if there were much more CO2 overall back in 1980, and less today when there is a less frequent replenish rate? Here again speculation can detract from the right answer, since this is a must be true question. Consequently, it's essential to stay only within what is permitted by the statements we are given. And those statements include one that is unequivocal: "The less frequently cabin air is replenished in a plane in flight, the higher the level of carbon dioxide."

The "similar" in the last sentence feels like it protects the answer choice around questions about the flight itself

Yes, I agree that the "similar flight" language functions to protect the answer choice. Without that, there might be a risk that a new variable is being introduced, namely, a different aircraft. Instead of that, the answer choice seems phrased so as to affirm that the newer flight is otherwise "similar."