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.
OA E
Source: GMAT Prep
For what percent of those tested for a certain infection was
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The best way to approach this question is with a DOUBLE SET MATRIX.
There are 2 relevant questions here:
1. Does a person have the infection or not?
2. Have they tested positive or not?
Accurate results will be those who (had it & tested positive) + (didn't have it and tested negative) as a percentage of all people tested.
Now apply the information from the statements one at a time:
(1) Of those who tested positive for the infection,1/8 did not have the infection.
Let x = total of those who tested positive. Convert 1/8 to 12.5%:
This is clearly not sufficient to answer the question.
Note: be sure to erase info from statement 1 before evaluating statement 2.
(2) Of those tested for the infection, 90 percent tested negative.
This tells us nothing about who had / didn't have the infection. Insufficient.
(1) & (2) Together:
We now know that x = 10% of the total:
We still have no information about those who tested negative & didn't have the infection, though. So we do not have sufficient information.
The answer is E.
There are 2 relevant questions here:
1. Does a person have the infection or not?
2. Have they tested positive or not?
Accurate results will be those who (had it & tested positive) + (didn't have it and tested negative) as a percentage of all people tested.
Now apply the information from the statements one at a time:
(1) Of those who tested positive for the infection,1/8 did not have the infection.
Let x = total of those who tested positive. Convert 1/8 to 12.5%:
This is clearly not sufficient to answer the question.
Note: be sure to erase info from statement 1 before evaluating statement 2.
(2) Of those tested for the infection, 90 percent tested negative.
This tells us nothing about who had / didn't have the infection. Insufficient.
(1) & (2) Together:
We now know that x = 10% of the total:
We still have no information about those who tested negative & didn't have the infection, though. So we do not have sufficient information.
The answer is E.
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
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- ceilidh.erickson
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For more on how to use Double Set Matrices for similar problems, see:
https://www.beatthegmat.com/in-a-produc ... tml#818274
https://www.beatthegmat.com/retailers-q ... tml#809549
https://www.beatthegmat.com/in-a-class- ... tml#802582
https://www.beatthegmat.com/jefferson-s ... tml#708717
https://www.beatthegmat.com/sandwich-t2 ... tml#730500
https://www.beatthegmat.com/ds-question ... tml#677080
https://www.beatthegmat.com/survery-res ... tml#576105
https://www.beatthegmat.com/rainbow-tro ... tml#555603
https://www.beatthegmat.com/in-a-produc ... tml#818274
https://www.beatthegmat.com/retailers-q ... tml#809549
https://www.beatthegmat.com/in-a-class- ... tml#802582
https://www.beatthegmat.com/jefferson-s ... tml#708717
https://www.beatthegmat.com/sandwich-t2 ... tml#730500
https://www.beatthegmat.com/ds-question ... tml#677080
https://www.beatthegmat.com/survery-res ... tml#576105
https://www.beatthegmat.com/rainbow-tro ... tml#555603
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
EdM in Mind, Brain, and Education
Harvard Graduate School of Education