This is an inference question, and we don't have a nice conclusion to use as a starting point. Instead, let's make sure we clearly understand the given information, paying attention to little details and modifiers as we go:

• "Transportation expenses accounted for a large portion of the total dollar amount spent on trips for pleasure by residents of the United States in 1997." This statement has lots of important details, so don't skim over them. TE accounted for a LARGE portion, but we don't know how large. We cannot say that TE accounted for the LARGEST portion or even for MOST of the total. Also, keep in mind that we are only talking about trips for pleasure by US residents.
• "About half of the total dollar amount spent on the transportation was airfare." So of the TE described above, about half of it was spent on airfare. The other half comprised other transportation expenses (perhaps cars/fuel, buses, trains, etc).
• "The large majority of US residents who took trips for pleasure in 1997 did not travel by airplane but used other means of transportation." - There is no numerical cutoff for a "large" majority but if the numbers were close (i.e. a 49%-51% split), it would make more sense to call it a "slim" majority. For example, if 499 people like Coke and 501 like Pepsi, then most people like Pepsi and the majority of people like Pepsi. But does a large majority prefer Pepsi? Not in this case because the difference is very small. If 800 people like Coke and 200 like Pepsi, then we could say that the large majority of people surveyed like Coke. Again, there really isn't any absolute rule for the numerical cutoff, but if we want to use "large majority", there should be a significant difference. So this statement tells us that a lot more people did NOT travel by airplane but used other means of transportation.

If the statements above are true, which of the following must also be true about United States residents who took trips for pleasure in 1997?


The passage doesn't say anything about WHY people chose air travel or other means of transportation. In fact, the numbers seem to suggest that those who traveled by airplane had HIGHER average TE than people who did not travel by airplane. Flying may have been the more expensive option, but people may have chosen it because, for example, it was much faster, more convenient, more comfortable, etc. Choice (A) can be eliminated.


Again, the passage doesn't say anything about WHY people chose certain means of transportation. It is certainly possible that several modes of transportation were available and people chose to fly for a variety of reasons (speed, convenience, comfort, etc). Choice (B) is not necessarily true and can be eliminated.


The problem with choice (C) is the "per mile traveled" part. Those who traveled by airplane may have spent more IN TOTAL on transportation than did those who used other means of transportation, but that does not necessarily mean they spent more PER MILE. For example, those who chose to fly may have traveled thousands of miles on average to reach their destinations while those who did not fly may have traveled only tens or hundreds of miles on average. We cannot infer that this is true, so eliminate (C).



About half of the TE was spent on airfare and about half of the TE was spent on other transportation costs (i.e. cars/fuel, buses, trains, etc.). But a LARGE MAJORITY of the people who took trips for pleasure did NOT travel by airplane. How could this be true?

We are told that the amount spent on airfare was about the same as the amount spent on other transportation costs. So picture two equal bars on a bar graph. If the number of people traveling by airplane was about the same as the number of people using other means of transportation, then we would divide the bars by roughly the same number to get the average TE for both groups. But we know that the number of people who did NOT travel by plane was much higher than the number who did travel by plane (the large majority did not travel by airplane). That means we have to divide the non-airfare bar by a much HIGHER number than the airfare bar to get the average TE for each group. That means that the average TE would be much higher for the airfare group (because we divided by a smaller number). Choice (D) has to be true, so keep this one.


The amount that those who traveled by airplane spent on other means of transportation (i.e. rental cars, etc.) may have only been a small fraction of what they spent on airfare. Most of the non-airfare TE were likely incurred by the large majority who did NOT travel by airplane. Choice (E) does not have to be true and can be eliminated.

Choice (D) is the only one that has to be true.

GMATNinja,

Thank you for the awesome explanation.
I just had a doubt with C. I understand the error with the 'per mile traveled' part. As per the explanation, those who traveled by airplane may have spent more IN TOTAL on transportation than did those who used other means of transportation.
The argument, however, says "about half of the total dollar amount spent on the transportation was airfare". This means roughly 50 percent. I thought that this could be 50 percent or slightly less than 50 percent. Then how is that there can be a case where "those who traveled by airplane may have spent MORE in total on transportation than did those who used other means of transportation". More importantly, can roughly half mean more than half?
Also, I am unsure that any inference can be drawn regarding the airfare portion of TE being more or less than the other means of transportation portion of TE. As per my understanding, we need the word 'average' as used in D to make it a valid inference.

Thanks and Regards,
Udit

(D) Overall, people who did not travel by airplane had lower average transportation expenses than people who did.

(E) Those who traveled by airplane spent about as much, on average, on other means of transportation as they did on airfare.

Say: GroupA: Airfare 100$ ; other TE 100$ (total people : 100)



TE( travel by plane)= 200/100 = 2$
Case1: 100/500 = 0.2$ [GroupB : Other mode 50$; other TE: 50$ ( total people 500) or GroupB : Other mode 20$; other TE: 80$ ( total people 500) or GroupB : Other mode 80$; other TE: 20$ ( total people 500)]
Case2: 200/500 = 0.4$ [GroupB : Other mode 100$; other TE: 100$ ( total people 500) or 50:150 or 150:50]
Case3: 500/500 = 1$ [GroupB : Other mode 250$; other TE: 250$ ( total people 500) or 200:300 or 300:200]
Case4: 1000/500 = 2$ [GroupB : Other mode 500$; other TE: 500$ ( total people 500) or 400:600 or 600:400]

Case 3 and case 4: Doesn't satisfy

Wrong


Those who traveled by airplane = 100 people spent on average other means of transportation ( 100$) as they did on airfare(100$)
average airfare: 100/100( airfare)= 1
average no-airfare= 100/100 = 1

Same 1:1
correct


Sir , whats wrong in my D and E.

I chose E over D.
What am I missing. I checked above explanations
Doubts for D: why non- airfare expense can not be more than airfare? people who didnt travel by air may have spent more while travelling by train or car . Airfare is not always expensive than other modes of transportation
Doubts for E: Why people considered the amount spent on other modes of travel of group who didnt use air. Option E specifically asks average of people spent on airfare with other modes. Why do we need to consider expensiture o other group whih is not asked for.

Please correct AndrewN sir GMATNinja

Transportation expenses accounted for a large portion of the total dollar amount spent on trips for pleasure by residents of the United States in 1997, and about half of the total dollar amount spent on the transportation was airfare. However, the large majority of United States residents who took trips for pleasure in 1997 did not travel by airplane but used other means of transportation.

If the statements above are true, which of the following must also be true about United States residents who took trips for pleasure in 1997?

(D) Overall, people who did not travel by airplane had lower average transportation expenses than people who did.

(E) Those who traveled by airplane spent about as much, on average, on other means of transportation as they did on airfare.

I think you have lost sight of the passage, imSKR. You know by now that I recommend a streamlined approach that leans heavily on exactly what the passage says. When you create a scaffolding around a half truth, you still get an incorrect answer. How about we approach these two answer choices by quoting the passage directly?


What do we know about people who did not travel by airplane? The last sentence of the passage tells us that this group represents the large majority of travelers. Since the first sentence tells us that about half of the total dollar amount spent on the transportation was airfare, we can deduce that within that other half of transportation expenses would lie the total dollar amount spent by our target group, those who did not travel by airplane. Stitched together, we can say with certainty that more of one group of travelers spent no more money on transportation expenses than did another group, even if the transportation expenses were the same on the whole. Finally, when you divide either the same amount or a lesser amount by a greater number (of travelers, in this case), the average will always be lower. Thus, we cannot argue against (D).


Where do we get any information in the passage about those who traveled by airplane also spending on other means of transportation? Not in the first sentence, and not in the second either. So, in short, we cannot speculate on how much this group of people may have spent on transportation outside of airfare. There is nothing to lean on in the passage, the opposite of what we want in a must be true answer. This should be an easy elimination.

I hope you will take the time to let these points sink in. Sometimes when you want something to be true, you (the general you) close your mind to other possibilities and forget to seek out evidence to support your idea.

Thank you for thinking to ask me about this one.

- Andrew

Thanks AndrewN sir, I realized the mistake in understanding the 1st sentence, thus I got answer E but not D

What I read before:
Transportation expenses accounted for a large portion of the total dollar amount spent on trips for pleasure by residents of the United States in 1997, and about half of the total dollar amount spent ( of Transportation expenses ) on the transportation was airfare.

What is given:
Transportation expenses accounted for a large portion of the total dollar amount spent on trips for pleasure by residents of the United States in 1997, and about half of the total dollar amount spent ( of the total dollar amount spent on trips for pleasure by residents of the United States in 1997, ) on the transportation was airfare.

Transportation expenses =A: Spent on Trips ( large proportion) + B: Other transportation ( smaller proportion)

Half of the amount of A = airfare on trips = A1
Half of amount of A= non Airfare on trips= A2

2nd statement: X (800: large majority>> Y( 200)
D says: A1/800< A2/200 = absolutely true

Now My understanding is right? So Lesson learnt: Be more specific.

Transportation expenses accounted for a large portion of the total dollar amount spent on trips for pleasure by residents of the United States in 1997, and about half of the total dollar amount spent on the transportation was airfare. However, the large majority of United States residents who took trips for pleasure in 1997 did not travel by airplane but used other means of transportation.

If the statements above are true, which of the following must also be true about United States residents who took trips for pleasure in 1997?


(A) Most of those who traveled by airplane did so because the airfare to their destination was lower than the cost of other available means of transportation.

(B) Most of those who traveled by airplane did so because other means of transportation to their destinations were unavailable.

(C) Per mile traveled, those who traveled by airplane tended to spend more on transportation to their destination than did those who used other means of transportation.

(D) Overall, people who did not travel by airplane had lower average transportation expenses than people who did.

(E) Those who traveled by airplane spent about as much, on average, on other means of transportation as they did on airfare.