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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 If √k is not an integer, then is k a prime number? This topic has 3 expert replies and 0 member replies Top Member If √k is not an integer, then is k a prime number? Timer 00:00 Your Answer A B C D E Global Stats Difficult If √k is not an integer, then is k a prime number? (1) k < 10 (2) k < 5 OA E Source: Magoosh GMAT/MBA Expert GMAT Instructor Joined 02 Jun 2008 Posted: 2475 messages Followed by: 350 members Upvotes: 1090 GMAT Score: 780 Using both statements, k can be 2, and thus prime, or -1, and not prime, so the answer is E. _________________ If you are looking for online GMAT math tutoring, or if you are interested in buying my advanced Quant books and problem sets, please contact me at ianstewartgmat at gmail.com GMAT/MBA Expert GMAT Instructor Joined 08 Dec 2008 Posted: 12995 messages Followed by: 1250 members Upvotes: 5254 GMAT Score: 770 BTGmoderatorDC wrote: If √k is not an integer, then is k a prime number? (1) k < 10 (2) k < 5 Given: √k is not an integer Target question: Is k a prime number? Statement 1: k < 10 Let's TEST some values. There are several values of k that satisfy statement 1. Here are two: Case a: k = 1.3 (√1.3 is not an integer). In this case, the answer to the target question is NO, k is NOT a prime number Case b: k = 3 (√3 is not an integer). In this case, the answer to the target question is YES, k IS a prime number Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT Statement 2: k < 5 Let's TEST some values. There are several values of k that satisfy statement 2. Here are two: Case a: k = 1.3 (√1.3 is not an integer). In this case, the answer to the target question is NO, k is NOT a prime number Case b: k = 3 (√3 is not an integer). In this case, the answer to the target question is YES, k IS a prime number Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT Statements 1 and 2 combined IMPORTANT: Notice that I was able to use the same counter-examples to show that each statement ALONE is not sufficient. So, the same counter-examples will satisfy the two statements COMBINED. In other words, Case a: k = 1.3 (√1.3 is not an integer). In this case, the answer to the target question is NO, k is NOT a prime number Case b: k = 3 (√3 is not an integer). In this case, the answer to the target question is YES, k IS a prime number Since we cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT Answer: E Cheers, Brent _________________ Brent Hanneson – 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 GMAT’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 BTGmoderatorDC wrote: If √k is not an integer, then is k a prime number? (1) k < 10 (2) k < 5 OA E Source: Magoosh Let's take each statement one by one. (1) k < 10 Case 1: Say k = 8, not prime We have √k = √8 = not an integer Case 2: Say k = 7, prime We have √k = √7 = not an integer No unique answer. Insufficient. (2) k < 5 Case 1: Say k = 4,5, not prime (note that it is not given that k is an integer) We have √k = √4.5 = not an integer Case 2: Say k = 3, prime We have √k = √3 = not an integer No unique answer. Insufficient. (1) and (2) together Cases discussed in Statement 2 are applicable here too. Insufficient. The correct answer: E Hope this helps! -Jay _________________ Manhattan Review GMAT Prep Locations: Manhattan GMAT Classes | GMAT Prep Courses Dubai | LSAT Prep Courses Hong Kong | Singapore SAT Prep Classes | and many more... Schedule your free consultation with an experienced GMAT Prep Advisor! Click here. • Get 300+ Practice Questions 25 Video lessons and 6 Webinars for FREE Available with Beat the GMAT members only code • Free Trial & Practice Exam BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • Award-winning private GMAT tutoring Register now and save up to$200

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