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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 ## gmat prep ##### This topic has 3 member replies ## gmat prep If X is a positive integer, what is the Least common multiple of X, 6, 9 1. the least common mulitple of x and 6 is 30 2. the least common multiple of x and 9 is 45 the OA is D but i got it to be C because I thought X could be either 5 or 15. someone help? Junior | Next Rank: 30 Posts Joined 08 Aug 2008 Posted: 14 messages Upvotes: 12 Mclaughlin wrote: If X is a positive integer, what is the Least common multiple of X, 6, 9 1. the least common mulitple of x and 6 is 30 2. the least common multiple of x and 9 is 45 the OA is D but i got it to be C because I thought X could be either 5 or 15. someone help? I actually got the same answer for the same reason. X could be either 5 or 15. Interesting! Newbie | Next Rank: 10 Posts Joined 19 Jul 2008 Posted: 7 messages Upvotes: 1 X could be 5 or 15 but the LCM of X,6,9 doesn't change if X is 5,15 or even 45. Hence IMO D. Please correct me if I'm wrong. Legendary Member Joined 16 Aug 2008 Posted: 891 messages Followed by: 1 members Upvotes: 27 Target GMAT Score: 750) GMAT Score: 660( I agree with D Question is not about the value of x, it is about the LCM of three intergers The key here is prime factorisation rephrasing the main statement: What is LCM of x, 2*3 (6=2*3), and 3^2 (9=3*3) (1) LCM of x and 2*3 is 30. Factoring 30=2*3*5 this means that x has 5 as a factor. x can contain 2 and 3 but not necessary answering the main question: LCM of 2*3, 3^3 and x is 2*3^2*5=90 Let's check x=5. LCM of 5, 6 and 9 is 90 x=10. LCM = 90 x=15. LCM = 90 SUFF (2) Using the same logic LCM of x and 3^2 is 45 45 = 3^2*5 x has 5 as a factor LCM of 5, 6 and 9 is 90 SUFF Answer D Remember, that LCM of 2 or more numbers is a product of all prime numbers, included into prime factorization at least one of these numbers, raised to the highest of two powers GCD of 2 or more numbers is a product of prime numbers, included into prime factorization of all numbers, and raised to the smallest of two powers • 1 Hour Free BEAT THE GMAT EXCLUSIVE 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 • 5 Day FREE Trial Study Smarter, Not Harder Available with Beat the GMAT members only code • Get 300+ Practice Questions 25 Video lessons and 6 Webinars for FREE Available with Beat the GMAT members only code • Free Practice Test & Review How would you score if you took the GMAT Available with Beat the GMAT members only code • Magoosh Study with Magoosh GMAT prep 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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