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gmatbull
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.

For my simplicity I took a smart number as 80.
In the attached diagram, we are supposed to find the red area.

We don't have sufficient information to find the red area.
+1E
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isn't this question asking for 2 variables? I got the answer E
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gmatbull
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.

Statement One Alone:

Of those who tested positive for the infection,1/8 did not have the infection.

We can let the total people who tested positive for the infection = p; thus, (7/8)p tested positive and had the infection. However, since we know nothing about those who tested negative, we cannot determine an answer. Statement one alone is not sufficient to answer the question.

Statement Two Alone:

Of those tested for the infection, 90 percent tested negative.

Using the information in statement two, we know that 90 percent tested negative and 10 percent tested positive. However, we still do not have enough information to answer the question.

Statements One and Two Together:

Using both statements, we still do not have information about those who did not have the infection and tested negative; we cannot determine an answer.

Answer: E
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gmatbull
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.


hey there :)

why no one used overlapping sets formula ?

chetan2u, VeritasKarishma any idea when do we need to use matrix vs overlapping circles ?


have a good Sunday :-)
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gmatbull
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.


hey there :)

why no one used overlapping sets formula ?

chetan2u, VeritasKarishma any idea when do we need to use matrix vs overlapping circles ?


have a good Sunday :-)

Hi...

Overlapping sets is best used when you have two unknowns..
Say in this question we just had positive and accurate results.so this would have meant two circles one for accurate and other for positive and overlapped area would give us the positive results that were accurately determined.
However here there are four unknowns - accurately determined positive, inaccurately determined positive, accurately determined negative and inaccurately determined negative.
So a matrix 2*2 is the best here
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Bunuel,
I'm seeking expert guidance on determining exactly which "boxes" the problem is referring to. Although many solutions say it is the total of Had Ifection, in the attached matrix, I suspect the phrasing suggests that only the diagonal entries should be considered. Could you help clarify this interpretation?

Thanks in advance.
gmatbull
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 who tested for the infection, 90 percent tested negative.


ID 04552

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