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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 ## Integers tagged by: BTGmoderatorRO ##### This topic has 1 expert reply and 0 member replies ## Integers The function f is defined for all positive integers n by the following rule: f(n) is the number of positive integers each of which is less than n and has no positive factor in common with n other than 1. If p is any number then f(p) = (a) p-1 (b) p-2 (c) $$\frac{p+1}{2}$$ (d) $$\frac{p-1}{2}$$ (e) 2 OA is A Can an Expert give me the mathematical approach to solve this question? Thanks in anticipation ### GMAT/MBA Expert Elite Legendary Member Joined 23 Jun 2013 Posted: 9939 messages Followed by: 492 members Upvotes: 2867 GMAT Score: 800 Hi Roland2rule, To start, this question has a 'typo' in it - P must be a PRIME number (NOT "any number"). We're told that the function f is defined for all positive integers N by the following rule: f(N) is the number of positive integers each of which is LESS than N and has no positive factor in common with N other than 1. We're asked for the value of f(P) if P is a PRIME number. This question can be solved by TESTing VALUES. IF.... P = 5 then the positive integers that are LESS than 5 and have NO factors in common with 5 (other than the number 1) are 1, 2, 3 and 4. Thus, the f(5) = 4, so we're looking for an answer that equals 4 when we plug P=5 into the answer choices. There's only one answer that matches. Final Answer: A GMAT assassins aren't born, they're made, Rich _________________ Contact Rich at Rich.C@empowergmat.com • Magoosh Study with Magoosh GMAT prep 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 Trial & Practice Exam BEAT THE GMAT EXCLUSIVE 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 • 5 Day FREE Trial Study Smarter, Not Harder Available with Beat the GMAT members only code • FREE GMAT Exam Know how you'd score today for$0

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