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100 points for $49 worth of Veritas practice GMATs FREE VERITAS PRACTICE GMAT EXAMS Earn 10 Points Per Post Earn 10 Points Per Thanks Earn 10 Points Per Upvote ## For what percent of those tested for a certain infection was ##### This topic has 2 expert replies and 0 member replies ### Top Member ## For what percent of those tested for a certain infection was ## Timer 00:00 ## Your Answer A B C D E ## Global Stats Difficult 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 ### GMAT/MBA Expert GMAT Instructor Joined 04 Dec 2012 Posted: 1996 messages Followed by: 237 members Upvotes: 1443 Top Reply _________________ Ceilidh Erickson Manhattan Prep GMAT & GRE instructor EdM in Mind, Brain, and Education Harvard Graduate School of Education Manhattan Prep instructors all have 99th+ percentile scores and expert teaching experience. Sign up for a FREE TRIAL, and learn why we have the highest ratings in the GMAT industry! Free Manhattan Prep online events - The first class of every online Manhattan Prep course is free. Classes start every week. ### GMAT/MBA Expert GMAT Instructor Joined 04 Dec 2012 Posted: 1996 messages Followed by: 237 members Upvotes: 1443 Top Reply 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. _________________ Ceilidh Erickson Manhattan Prep GMAT & GRE instructor EdM in Mind, Brain, and Education Harvard Graduate School of Education Manhattan Prep instructors all have 99th+ percentile scores and expert teaching experience. Sign up for a FREE TRIAL, and learn why we have the highest ratings in the GMAT industry! Free Manhattan Prep online events - The first class of every online Manhattan Prep course is free. Classes start every week. • Free Practice Test & Review How would you score if you took the GMAT Available with Beat the GMAT members only code • Award-winning private GMAT tutoring Register now and save up to$200

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