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# When 100 people who have not used cocaine are tested for

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Senior Manager
Joined: 05 May 2003
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When 100 people who have not used cocaine are tested for [#permalink]  19 Aug 2004, 11:25
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5% (low)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
23. 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.
Senior Manager
Joined: 25 Jul 2004
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C. If there are only 5 cocaine users in the country, the vast majority of those who test positive WILL not be cocaine users (they will be in the 5% error group)
GMAT Club Legend
Joined: 15 Dec 2003
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Clearly C. Proportion user/non-user not taken into account. Typical GMAT type question. I anticipated the answer before reading the choices.
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Paul

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C for me too. I think this is the sort of thing they test in AWA too, giving you a question stem invovlving surveys but not stating the size of the population invovled in their surveys.
Senior Manager
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I think it should be B.
I will attempt to explain If iam correct.
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