BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

For what percent of those tested for a certain infection was

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Moderator
Posts: 7187
Joined: Thu Sep 07, 2017 4:43 pm
Followed by:23 members

For what percent of those tested for a certain infection was

by BTGmoderatorDC » Thu Aug 09, 2018 2:51 pm

Timer

00:00

Your Answer

A

B

C

D

E

Global Stats

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
Top
Source: — Data Sufficiency |
User avatar
GMAT Instructor
Posts: 2095
Joined: Tue Dec 04, 2012 3:22 pm
Thanked: 1443 times
Followed by:247 members

by ceilidh.erickson » Tue Aug 21, 2018 11:21 am

Timer

00:00

Your Answer

A

B

C

D

E

Global Stats

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?

Image

Accurate results will be those who (had it & tested positive) + (didn't have it and tested negative) as a percentage of all people tested.

Image

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%:

Image

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.

Image

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:

Image

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
Top
User avatar
GMAT Instructor
Posts: 2095
Joined: Tue Dec 04, 2012 3:22 pm
Thanked: 1443 times
Followed by:247 members

by ceilidh.erickson » Tue Aug 21, 2018 11:23 am

Timer

00:00

Your Answer

A

B

C

D

E

Global Stats

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
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
Top
Post new topic Post Reply
• Page 1 of 1