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

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Manager
Joined: 20 Dec 2013
Posts: 230
Location: India
Re: When 100 people who have not used cocaine are tested for  [#permalink]

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02 Jan 2014, 23:44
I choose C.We clearly need to find out the proportion of people who used cocaine in order to infer whether 'the vast majority' actually used it or not.

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Director
Joined: 17 Dec 2012
Posts: 630
Location: India
Re: When 100 people who have not used cocaine are tested for  [#permalink]

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03 Jan 2014, 22:19
nitya34 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.

Negate the conclusion:

It is: The vast majority of those who test positive out of a random group of people would not have used cocaine.

Since this a find the flaw question we have to select a choice which can weaken the conclusion .

So let us consider this as a weaken question first and so see which choice offers the best explanation for the negated conclusion.

Choice C because a particular case of it which is , a small proportion of the population take cocaine, offers the best explanation for the negated conclusion.

This is because assume 10000 people are tested . A small proportion of that population be 1% i.e, 100 people take cocaine. 99 of them would test positive. Of the remaining 9900 people 5%, i.e., 445 would test positive. So we see the majority of those who test positive are those who had not used cocaine.
i.e, if
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Manager
Joined: 14 Apr 2015
Posts: 53
Re: When 100 people who have not used cocaine are tested for  [#permalink]

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23 Nov 2015, 23:02
neelabhmahesh wrote:
The answer in my stuff says E is the answer. If it wrong pls tell me.

The answer is C, not E.
In the argument, we make a conclusion about the majority who might be taking cocaine. E talks about the advocating the use of the tests. So, E is irrelevant.
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Re: When 100 people who have not used cocaine are tested for  [#permalink]

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06 Jul 2018, 19:55
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Re: When 100 people who have not used cocaine are tested for &nbs [#permalink] 06 Jul 2018, 19:55

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

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