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When 100 people who have not used cocaine are tested for

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Re: When 100 people who have not used cocaine are tested for [#permalink]

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New post 30 Oct 2013, 22:11
This is my understand ding of the passage. Say there are 100 people if u choose say 50 people from them randomly. there will two groups 1) who test positive 2) who don't test positive
the argument says that of those who test positive (group 1), majority are cocaine users.
what you guys are saying is that argument says that majority of the people randomly picked from the crowd are cocaine users. In that case D stands true but not otherwise is what I feel. Please correct me if I am wrong.
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Re: When 100 people who have not used cocaine are tested for [#permalink]

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New post 01 Jan 2014, 15:04
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.


Hi,

For me it is clearly C.

Why? Well because if 99.99999% Of 1000000 of a population never took cocaine but only 100 has. Than (1000000*0.05 = 50000 who did not take drug and you have on the other side 99 who take drug)

Than with this demonstration, the argument is totaly flawed.

You need to take into account the proportion or the part of the population actually taking drugs.

Answer C.
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Re: When 100 people who have not used cocaine are tested for [#permalink]

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New post 03 Jan 2014, 00:44
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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Re: When 100 people who have not used cocaine are tested for [#permalink]

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New post 03 Jan 2014, 23:19
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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Re: When 100 people who have not used cocaine are tested for [#permalink]

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New post 24 Nov 2015, 00:02
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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New post 06 Jul 2018, 20:55
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Re: When 100 people who have not used cocaine are tested for   [#permalink] 06 Jul 2018, 20:55

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