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When 100 people who have not used cocaine are tested for

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When 100 people who have not used cocaine are tested for [#permalink] New post 06 Dec 2012, 01:47
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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.

OA is
[Reveal] Spoiler:
C

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Last edited by Marcab on 07 Dec 2012, 19:42, edited 1 time in total.
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Re: Cocaine test [#permalink] New post 06 Dec 2012, 02:11
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Let us have some perpective from others as well.
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Re: Cocaine test [#permalink] New post 06 Dec 2012, 05:02
Marcab gr8 question indeed.....

I would like to go with B

Conclusion; 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.

premise; 100 non users tested 5 found +ve; 100 users tested 99 found +ve. Conclusion generalizes vast majority tested +ve will be ppl who have used coc...

B and D are contenders

(D) ignores the fact that some cocaine users do not test positive.: Thats true but we have to find the reasoning error in the conclusion and conclusion states vast majority of those tested +ve are ppl who have used coc..
(B) attributes to every member of the population the properties of the average member of the population. This is true as there is transition in the use of word average to people in the argument.
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Re: Cocaine test [#permalink] New post 07 Dec 2012, 17:14
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Thanks for the question +1 Kudos :) . I was stuck between B and C and I have chosen C.

The testing case implemented on the mere users or the mere not users. It does not mention about the population. It says 100 people who did not use cocainne, the 5 will test positive and of the whom used cocaine 99% will test positive. So what if there are 1.000 cocaine users out of 1.000.000 people. It says a randomly chosen group it does not say 50 cocaine users and 50 not cocaine users. So it is unclear what is our big picture. If the case is above the percentages will be around 5% . But what if 500.000 out of 1.000.000 people(hypothetically) used cocaine than it would be around 52%.

Marcab 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.

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Re: Cocaine test   [#permalink] 07 Dec 2012, 17:14
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