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cocaine use

by ankita1709 » Tue May 29, 2012 3:17 am
When 100 people who have not used cocaine are tested for cocaine use, on average only 5 will test positive. By contrast, of every 100 people who have used cocaine 99 will test positive. Thus, when a randomly chosen group of people is tested for cocaine use, the vast majority of those who test positive will be people who have used cocaine.

A reasoning error in the argument is that the argument
(A) attempts to infer a value judgment from purely factual premises
(B) attributes to every member of the population the properties of the average member of the population
(C) fails to take into account what proportion of the population have used cocaine
(D) ignores the fact that some cocaine users do not test positive
(E) advocates testing people for cocaine use when there is no reason to suspect that they have used cocaine.

The answer I have is C but it seems incorrect to me.
Can anyone please help me with the right answer
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by Kasia@EconomistGMAT » Tue May 29, 2012 3:33 am
Do you mean that this answer is provided as the OA?
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by ankita1709 » Tue May 29, 2012 4:05 am
Kasia@MasterGMAT wrote:Do you mean that this answer is provided as the OA?
I can't trust the source of this answer so can't say this is the right answer
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by Ashujain » Tue May 29, 2012 4:51 am
ankita1709 wrote:When 100 people who have not used cocaine are tested for cocaine use, on average only 5 will test positive. By contrast, of every 100 people who have used cocaine 99 will test positive. Thus, when a randomly chosen group of people is tested for cocaine use, the vast majority of those who test positive will be people who have used cocaine.

A reasoning error in the argument is that the argument
(A) attempts to infer a value judgment from purely factual premises
(B) attributes to every member of the population the properties of the average member of the population
(C) fails to take into account what proportion of the population have used cocaine
(D) ignores the fact that some cocaine users do not test positive
(E) advocates testing people for cocaine use when there is no reason to suspect that they have used cocaine.

The answer I have is C but it seems incorrect to me.
Can anyone please help me with the right answer
The answer should be C. Let me explain:
Test involves randomly selected people and in this group there can be people who have not used cocaine but as per 1st sentence of the argument even they can be tested positive. So it is necessary that we know the proportion of the population who have used cocaine because only then we can conclude anything.

Kindly correct me if i am wrong.
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by ankita1709 » Tue May 29, 2012 6:55 am
Ashujain wrote:
The answer should be C. Let me explain:
Test involves randomly selected people and in this group there can be people who have not used cocaine but as per 1st sentence of the argument even they can be tested positive. So it is necessary that we know the proportion of the population who have used cocaine because only then we can conclude anything.

Kindly correct me if i am wrong.
I agree with your reasoning but whats wrong with E
(E) advocates testing people for cocaine use when there is no reason to suspect that they have used cocaine.
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by GMAT Kolaveri » Tue May 29, 2012 8:25 am
ankita1709 wrote:
Ashujain wrote:
The answer should be C. Let me explain:
Test involves randomly selected people and in this group there can be people who have not used cocaine but as per 1st sentence of the argument even they can be tested positive. So it is necessary that we know the proportion of the population who have used cocaine because only then we can conclude anything.

Kindly correct me if i am wrong.
I agree with your reasoning but whats wrong with E
(E) advocates testing people for cocaine use when there is no reason to suspect that they have used cocaine.
E is not relevant to the question asked. question asks for the reasoning error in the argument.
Premise speaks about a specific group of people. by specific i mean we know exactly how many have taken cocaine and how many have not. From this argument we have jumped to a conclusion on a random set of people. by random i mean we dont have any idea on the number of people who ve taken cocaine and how many have not. this is the reasoning error which is pointed out in option C
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by Ashujain » Tue May 29, 2012 10:17 am
ankita1709 wrote:
Ashujain wrote:
The answer should be C. Let me explain:
Test involves randomly selected people and in this group there can be people who have not used cocaine but as per 1st sentence of the argument even they can be tested positive. So it is necessary that we know the proportion of the population who have used cocaine because only then we can conclude anything.

Kindly correct me if i am wrong.
I agree with your reasoning but whats wrong with E
(E) advocates testing people for cocaine use when there is no reason to suspect that they have used cocaine.
The question asks about the reasoning error but E talks about an error which has more to do with the moral or conscience of the people who are performing the tests. It is not a reasoning error.

Hope it helps!
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by jimmyjimmy » Sat Jun 02, 2012 8:25 pm
ws cnfused for C and E and took E but C seems fine after the above xplanation/..thanks guys..
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