The cost of owning a car in City X has dropped by 15 percent over the

Question

The cost of owning a car in City X has dropped by 15 percent over the past two years. In City Y, on the other hand, the cost of owning a car has increased by 65 percent over the same period of time. Therefore, today the cost of owning a car in City X must be lower than the cost of owning a car in City Y.

The argument is flawed primarily because the author

The argument is flawed primarily because the author

(A) does not provide the reason for the dramatic increase in the cost of owning a car in City Y
(B) does not provide any information about changes in the costs of owning a car in City X and City Y more than two years ago
(C) compares the cost of owning a car in two cities only
(D) does not distinguish between costs of owning different brands of cars
(E) assumes that the initial costs of owning a car in City X and City Y were about the same

Bunuel · Accepted Answer

OFFICIAL EXPLANATION

The cost of owning a car in City X has dropped by 15 percent over the past two years. In City Y, on the other hand, the cost of owning a car has increased by 65 percent over the same period of time. Therefore, today the cost of owning a car in City X must be lower than the cost of owning a car in City Y.

The argument is flawed primarily because the author

The argument is flawed primarily because the author

(A) does not provide the reason for the dramatic increase in the cost of owning a car in City Y

Incorrect

This is an Argument Flaw question. You are required to locate the inherent flaw in the argument's conclusion or its underlying assumption. In this argument, sentences 1 and 2 are premises, citing facts. Sentence 3 is the conclusion, as it begins with the conjunction Therefore:

Premise A: the cost of owning a car in City X has dropped by 15%
 + 
Premise B: the cost of owning a car in City Y has risen by 65%
 ≠
Conclusion: owning a car in City X is cheaper than it is in City Y

Since the conclusion does not refer to the reasons for the changes in costs, but rather to these changes only, failing to specify the reason for the increase in the cost of owning a car in City Y is not a flaw.

(B) does not provide any information about changes in the costs of owning a car in City X and City Y more than two years ago

Incorrect.

Giving more information about previous changes to the costs of owning cars in Cities X and Y would not help resolve the flaw in this argument; the conclusion of the argument relates to the absolute cost, whereas the premises describe changes (or trends) in this cost, which is unknown.

(C) compares the cost of owning a car in two cities only

Incorrect.

This could be the correct answer if the conclusion were more general, that is, if on the basis of the costs of owning a car in two cities, a conclusion about the cost of owning a car in other cities were drawn. However, both the premise and the conclusion are limited to the cost of owning a car in these specific two cities.

(D) does not distinguish between costs of owning different brands of cars

Incorrect.

Since both the premise and the conclusion do not deal with a specific brand of car but with cars in general, such a distinction is irrelevant.

(E) assumes that the initial costs of owning a car in City X and City Y were about the same

The fact that the cost in City X goes down and the cost in City Y goes up does not necessarily mean that the cost in City X is lower than the cost in City Y. For example, if the cost of owning a car in City Y was ten times cheaper ten years ago, the recent changes would still not make owning a car in City Y more expensive.

Sumi1010 · Answer

Flaw is nothing but questioning the assumptions that are required to keep the conclusion valid.

By eliminating the choices, we can see  only E makes some sense . 
However, E is not questioning the "actual assumption" and hence not an ideal flaw.

Let's see the cases

City X Initial City X today City Y Initial City Y today
------------------------------ ----------------------------
100 85 100 165
50 42.5 100 165 
150 127.5 100 165

In all the above cases, City X today < City Y today

Thus, the conclusion (today the cost of owning a car in City X must be lower than the cost of owning a car in City Y)
 is valid if
 85% of X <160% of Y
i.e. X < (160/85)Y
i.e., Initial cost of car in X < (32/17)times Initial cost of car in Y.

Thus, the actual assumption required to keep the conclusion valid is :
Initial cost of car in X < (32/17)times Initial cost of car in Y.

and NOT that 
initial costs of owning a car in City X and City Y were about the SAME.

IMO- this problem is not from an Official GMAT.

Sumi1010 · Answer

"if the cost of owning a car in City Y was  ten times  cheaper ten years ago, the recent changes would still not make owning a car in City Y more expensive."
If above is true then how can the flaw be : to assume that the initial costs of owning a car in City X and City Y were about the  same   ?
Could you help me understand?

winterschool · Answer

Sumi1010

cost of owning a car two years ago was same in both countries, than in X it dropped by 15% and in Y it increased by 65%
Now it is helpful to understand why E is correct

If cost of owning a car was different than cant say the conclusion

Sumi1010 · Answer

winterschool 
Agree. 
But, the conclusion is valid even if the cost of owning a car two years ago in X was  1.5 times  that in Y. 
IMO, there can be multiple assumptions in an argument, but those which are vital for the argument to survive are considered.
How can we ensure that - Considering the two costs  SAME  - is the assumption on which conclusion stands?

VerbalBot · Answer

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The cost of owning a car in City X has dropped by 15 percent over the

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The cost of owning a car in City X has dropped by 15 percent over the

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