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# For what percent of those tested for a certain infection was

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Manager
Joined: 23 Mar 2008
Posts: 218
For what percent of those tested for a certain infection was [#permalink]

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01 May 2008, 21:30
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For what percent of those tested for a certain infection was the test accurate; that is, positive for those who had the infection and negative for those who did not have the infection?

(1) Of those who tested positive for the infection,1/8 did not have the infection.
(2) Of those tested for the infection, 90 percent tested negative.

OPEN DISCUSSION OF THIS QUESTION IS HERE: for-what-percent-of-those-tested-for-a-certain-infection-145310.html
[Reveal] Spoiler: OA
Intern
Joined: 28 Apr 2008
Posts: 15

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01 May 2008, 21:44
E, because we still don't know the percent of inaccuracy for the negative group.
Manager
Joined: 06 Feb 2008
Posts: 85

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01 May 2008, 22:36
Should we assume negative tests are not 100% accurate since question does not say so anywhere explicitly...!!!
SVP
Joined: 28 Dec 2005
Posts: 1558

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02 May 2008, 04:46
C, but not sure. I think its c because we know how many people did not have it from stat 1, and from stat 2 we know how many people the test said did not have it.
CEO
Joined: 29 Mar 2007
Posts: 2559

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02 May 2008, 05:55
1
KUDOS
puma wrote:
For what percent of those tested for a certain infection was the test accurate; that is , positive for those who had the infection and negative for those who did not have the infection?

1) of those who tested positive for the infection, 1/8 did not have the infection.
2) of those tested for the infection, 90 percent tested negative.

Z--> .9z test negative so .1z test positive.

1/80z+ 7/80z =.1z

The answer should be E b/c we know nothing about the 90% who tested negative.
Current Student
Joined: 06 Sep 2013
Posts: 1997
Concentration: Finance
Re: For what percent of those tested for a certain infection was [#permalink]

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17 Oct 2013, 09:03
1
KUDOS
puma wrote:
For what percent of those tested for a certain infection was the test accurate; that is , positive for those who had the infection and negative for those who did not have the infection?

1) of those who tested positive for the infection, 1/8 did not have the infection.
2) of those tested for the infection, 90 percent tested negative.

Agree, and I think this problem is best solved with a Double-Matrix

Just use Positive/Negative and Tested Positive/Tested Negative for each axis.
Then you will see that we are actually lacking the ones who tested negative.

Try it and let me know
Hope it helps

Cheers
J
Math Expert
Joined: 02 Sep 2009
Posts: 39673
Re: For what percent of those tested for a certain infection was [#permalink]

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17 Oct 2013, 09:07
OPEN DISCUSSION OF THIS QUESTION IS HERE: for-what-percent-of-those-tested-for-a-certain-infection-145310.html
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Re: For what percent of those tested for a certain infection was   [#permalink] 17 Oct 2013, 09:07
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# For what percent of those tested for a certain infection was

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