My pick is D. Keyword is "per square mile".

Formula #1: Total car = (number of car/mile square) x (the number of mile squares)
All we know is "number of sport car per mile square --> At the first glance, we can NEITHER infer the total car NOR the number of mile squares (areas)

Formula #2: The number of sport car per mile square (*) = (1) number of sport car/mile square in downtown + (2) number of sport car/mile square in suburb + (3) number of sport car/mile square in exurb.

ANALYZE STIMULUS:

The number of sports cars per square mile is 40% greater in downtown Terrera than in downtown Goldsville. If the entire metropolitan area of each city is compared—which includes downtown as well as suburbs and exurbs—then the number of sports cars per square mile is 20% greater in Goldsville.

Based on the information above, which of the following can be inferred?

ANALYZE EACH OPTION:

A. There is a greater number of sports cars in the suburbs and exurbs of Goldsville than in those of Terrera.
Wrong. We can't infer the number of sport car if we don't know the area of each town.

B. In total, there is a greater number of sports cars in metropolitan Goldsville than in metropolitan Terrera.
Wrong. Same error as in A.

C. Metropolitan Goldsville covers a larger area than metropolitan Terrera.
Wrong. Stimulus does not mention that.

D. Per square mile, there are fewer sports cars in the exurbs and suburbs of Terrera than in those of Goldsville.
IMO, Correct.
FORMULA: The number of sport car per mile square (*) = (1) number of sport car/mile square in downtown + (2) number of sport car/mile square in suburb + (3) number of sport car/mile square in exurb.

Because Terrera has larger (1) than that of Goldsville ==> If Goldsville has larger (*) ==> Goldsville MUST have larger (2) and (3). If that's not the case, Goldsvill can't have 20% more sport car/mile square than the figure of Terrera.

E. The number of sports cars per square mile is greater in downtown Goldsville than in the suburbs and exurbs of Goldsville.
Wrong. We have no clue of how more/fewer sport car per mile square in downtown, exurb or suburb of Goldsville. All we know is the comparison between Goldsvill and Terrera. Thus, we can't infer that. E is wrong.

Waiting for OA.

In my opinion, D must be the answer. In percentage inference questions, if the argument discusses about precentages, over all absolute number of cars in the two cities cannot be inferred from the argument.

The number of sports cars per square mile is 40% greater in downtown Terrera than in downtown Goldsville. If the entire metropolitan area of each city is compared—which includes downtown as well as suburbs and exurbs—then the number of sports cars per square mile is 20% greater in Goldsville.

Based on the information above, which of the following can be inferred?

A. There is a greater number of sports cars in the suburbs and exurbs of Goldsville than in those of Terrera. Talking about absolute number of cars. Not correct.
B. In total, there is a greater number of sports cars in metropolitan Goldsville than in metropolitan Terrera. Same as A.
C. Metropolitan Goldsville covers a larger area than metropolitan Terrera. Again this choice compares absolute areas of the two cities. Not correct.
D. Per square mile, there are fewer sports cars in the exurbs and suburbs of Terrera than in those of Goldsville. This can be inferred. Since number of sports cars per square mile in downtown Terrera is 40% greater that that of in downtown Godsville and overall number of sports cars in metropolian city(including downtown, suburb and exurb) of Godsville is 20% greater than that of Terrera, it can be inferred that there are fewer sports cars per square mile in the exurbs and suburbs of Terrera than in those of Goldsville.
E. The number of sports cars per square mile is greater in downtown Goldsville than in the suburbs and exurbs of Goldsville. This cannot be true. The opposite of this could be true though. Hence not correct

Thanks for the helpful replies guys . I have posted the OA.

[fraction][/fraction]The number of sports cars per square mile is 40% greater in downtown Terrera than in downtown Goldsville. If the entire metropolitan area of each city is compared—which includes downtown as well as suburbs and exurbs—then the number of sports cars per square mile is 20% greater in Goldsville.

I ADOPT A SIMPLE METHOD FOR THESE QUESTIONS. Take 100 cars per square mile as a base for Downtown Goldsville......

Terrera Goldsville

140 100 ( Gives number of cars per square mile only taking downtown figures)
_ _
150 180 ( Gives number of cars per square mile including suburbs)
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10 80 ( Gives number of cars per square mile only taking suburb figures)
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ONLY NOW CAN THE FACTS HOLD...........
So inference is simple.............. ONLY D HOLDS.... THAT IS "Per square mile, there are fewer sports cars in the exurbs and suburbs of Terrera than in those of Goldsville. "

Hi, pqhai:
Can you explain for me the reason why

I think that number of car per mile square like average so we cannot sum 2 average in order to calculate the big average.

OA does not work, we can have 0 cars and a fixed suburb area for G town, while assigning 1 car and sufficiently large area to Town to bring down it's density to any number we want.

test takers should read carefully in real GMAT, I picked E because I read the option too fast. Also, because I know this is a common pattern in gmat, I already know the answer after I read the first sentence of the passage even though I have not done this question before (there are many similar questions with similar topics).

Official Explanation:

This is a tough question that not only deals with numbers vs. percents but also throws in downtown vs. the overall city, of which downtown is a part. The argument is as follows: There are more sports cars per mile in downtown T. than in downtown G. If the entire city is compared, however, the number of cars per square mile is greater in G.

(D) is correct because we know that T., per square mile, has more cars in downtown than G. but G. has more cars, per square mile, overall. Since the city is only made up of downtown, exurbs ,and suburbs, there must be more cars per square mile in the exurbs and suburbs of G. than in those of T.

(A) is tempting since we are led to believe that there are more total cars in G. than in T. Read carefully, though. More cars per square mile does not equal more total cars. In other words, it’s a question of density of sports cars in an area, not the total number of cars in that area. If metropolitan T. is much larger than metropolitan G., then it will have more total cars.

(B) is incorrect for the same reason as (A).

(C) is wrong because we only know about car per square mile (see (A)). We don’t know about total area.

(E) is wrong because the paragraph gives us nothing regarding the breakdown between the downtown vs. the non-downtown areas.
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