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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 08 Dec 2008 Posted: 12999 messages Followed by: 1250 members Upvotes: 5254 GMAT Score: 770 Top Reply I just want to point out that Jay has done a perfect job employing a technique known as the Double Matrix Method. This technique can be used for most questions featuring a population in which each member has two characteristics associated with it. Here, we have a population of patients, and the two characteristics are: - has infection or doesn't have infection - tested positive or tested negative This question type is VERY COMMON on the GMAT, so be sure to master the technique. To learn more about the Double Matrix Method, watch this video: http://www.gmatprepnow.com/module/gmat-word-problems?id=919 Once youâ€™re familiar with this technique, you can attempt these additional practice questions: Easy Problem Solving questions - http://www.beatthegmat.com/finance-majors-non-finance-majors-overlapping-set-question-t167425.html Medium Problem Solving questions - http://www.gmatprepnow.com/module/gmat-word-problems/video/920 - http://www.beatthegmat.com/posted-speed-limit-t272374.html - http://www.beatthegmat.com/motel-t271938.html - http://www.beatthegmat.com/of-the-applicants-passes-a-certain-test-15-t270255.html - http://www.beatthegmat.com/opening-night-and-late-patrons-t264869.html - http://www.beatthegmat.com/at-least-100-students-at-a-certain-high-school-study-japanes-t274669.html - http://www.beatthegmat.com/prblem-solving-t279424.html Difficult Problem Solving questions - http://www.gmatprepnow.com/module/gmat-word-problems/video/946 - http://www.beatthegmat.com/ratio-problem-t268339.html - http://www.beatthegmat.com/overlapping-sets-question-t265223.html - http://www.beatthegmat.com/fractions-t264254.html - http://www.beatthegmat.com/overlapping-sets-t264092.html - http://www.beatthegmat.com/mba/2011/05/09/random-double-matrix-question-2 Easy Data Sufficiency questions - http://www.gmatprepnow.com/module/gmat-word-problems/video/943 - http://www.beatthegmat.com/for-what-percent-of-those-tested-for-a-certain-t270596.html - http://www.beatthegmat.com/ds-quest-t187706.html Medium Data Sufficiency questions - http://www.beatthegmat.com/sets-matrix-ds-t271914.html - http://www.beatthegmat.com/each-of-people-voted-once-in-an-election-x-t271375.html - http://www.beatthegmat.com/a-manufacturer-t270331.html - http://www.beatthegmat.com/in-costume-for-halloween-t269355.html - http://www.beatthegmat.com/mba/2011/05/05/random-double-matrix-question-1 Difficult Data Sufficiency questions - https://youtu.be/dsCeqF9Kbk8 - http://www.beatthegmat.com/double-set-matrix-question-t271423.html - https://youtu.be/dOZ9KM1m5Hs - http://www.beatthegmat.com/sets-t269449.html - http://www.beatthegmat.com/mba/2011/05/16/random-double-matrix-question-3 Cheers, Brent _________________ Brent Hanneson â€“ Creator of GMATPrepNow.com Use my video course along with Sign up for free Question of the Day emails And check out all of these free resources GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMATâ€™s FREE 60-Day Study Guide and reach your target score in 2 months! GMAT/MBA Expert GMAT Instructor Joined 22 Aug 2016 Posted: 1984 messages Followed by: 30 members Upvotes: 470 Top Reply BTGmoderatorDC 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. OA E Source: GMAT Prep Pl. refer to the image below. The correct answer: E Hope this helps! -Jay _________________ Manhattan Review GRE Prep Locations: Manhattan GMAT | GMAT Prep Courses Riyadh | LSAT Prep Courses Orlando | Manhattan Prep SAT Courses | and many more... Schedule your free consultation with an experienced GMAT Prep Advisor! 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