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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 ## A certain junior class has 1000 students and a certain ##### This topic has 2 expert replies and 1 member reply ### Top Member ## A certain junior class has 1000 students and a certain ## Timer 00:00 ## Your Answer A B C D E ## Global Stats Difficult A certain junior class has 1000 students and a certain senior class has 800 students. Among these students, there are 60 siblings pairs each consisting of 1 junior and 1 senior. If 1 student is to be selected at random from each class, what is the probability that the 2 students selected will be a sibling pair? A. 3/40000 B. 1/3600 C. 9/2000 D. 1/60 E. 1/15 OA A Source: GMAT Prep ### Top Member Legendary Member Joined 29 Oct 2017 Posted: 965 messages Followed by: 4 members Top Reply Probability = number of ways to select 1 junior and 1 senior such that they make a sibling pair / number of ways to select 1 junior and 1 senior. = 60 / (1000*800) = 60 / 800000 = 3 / 400000 Or option A. Regards! ### GMAT/MBA Expert GMAT Instructor Joined 09 Apr 2015 Posted: 1465 messages Followed by: 18 members Upvotes: 39 Top Reply BTGmoderatorDC wrote: A certain junior class has 1000 students and a certain senior class has 800 students. Among these students, there are 60 siblings pairs each consisting of 1 junior and 1 senior. If 1 student is to be selected at random from each class, what is the probability that the 2 students selected will be a sibling pair? A. 3/40000 B. 1/3600 C. 9/2000 D. 1/60 E. 1/15 The probability of selecting any one sibling from the 60 sibling pairs in the junior class is 60/1000. Once that person is selected, the probability of selecting his or her sibling from the senior class is 1/800; thus, the probability of a selecting a sibling pair is: 60/1000 x 1/800 = 3/50 x 1/800 = 3/40000 Alternatively, the probability of selecting any one sibling from the 60 sibling pairs in the senior class is 60/800. Once that person is selected, the probability of selecting his or her sibling from the junior class is 1/1000; thus, the probability of a selecting a sibling pair is: 60/800 x 1/1000 = 3/40 x 1/1000 = 3/40000 Answer: A _________________ Jeffrey Miller Head of GMAT Instruction jeff@targettestprep.com See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews ### GMAT/MBA Expert Senior | Next Rank: 100 Posts Joined 19 Mar 2018 Posted: 38 messages Followed by: 1 members BTGmoderatorDC wrote: A certain junior class has 1000 students and a certain senior class has 800 students. Among these students, there are 60 siblings pairs each consisting of 1 junior and 1 senior. If 1 student is to be selected at random from each class, what is the probability that the 2 students selected will be a sibling pair? A. 3/40000 B. 1/3600 C. 9/2000 D. 1/60 E. 1/15 OA A Source: GMAT Prep There are 60 sibling pairs. The probability of selecting a sibling from the junior class is 60/1,000. The probability of selecting the other member of the sibling pair from the senior class is 1/800. The probability that both students selected will be a sibling pair is 60/1,000 * 1/800 = 3/40,000. The correct answer is choice A. Free GMAT Practice Test How can you improve your test score if you don't know your baseline score? Take a free online practice exam. Get started on achieving your dream score today! Sign up now. • Get 300+ Practice Questions 25 Video lessons and 6 Webinars for FREE Available with Beat the GMAT members only code • Free Veritas GMAT Class Experience Lesson 1 Live Free Available with Beat the GMAT members only code • 5-Day Free Trial 5-day free, full-access trial TTP Quant Available with Beat the GMAT members only code • Free Trial & Practice Exam BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • Magoosh Study with Magoosh GMAT prep Available with Beat the GMAT members only code • FREE GMAT Exam Know how you'd score today for$0

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