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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 ## OG PS #171 - Easy Sequence Question! tagged by: ##### This topic has 2 expert replies and 3 member replies ## OG PS #171 - Easy Sequence Question! ## Timer 00:00 ## Your Answer A B C D E ## Global Stats Difficult Hello all, I've never posted before, but I have a simple question about OG PS question #171. Question is: "What is the difference between the sixth and the fifth terms of the sequence 2, 4, 7.... whose nth term is n+2^n-1." According to the answer, you simply plug 6 and 5 into the term formula, but my question is why did they list seemingly random numbers first... I had assumed that those were the 1st, 2nd, and 3rd terms, I tried to plug them in as recursive numbers. If someone could explain that would be fantastic Thanks guys! Happy studying and/or happy tutoring! Kali Master | Next Rank: 500 Posts Joined 08 Dec 2010 Posted: 425 messages Followed by: 7 members Upvotes: 56 GMAT Score: 690 kalifalk wrote: Hello all, I've never posted before, but I have a simple question about OG PS question #171. Question is: "What is the difference between the sixth and the fifth terms of the sequence 2, 4, 7.... whose nth term is n+2^n-1." According to the answer, you simply plug 6 and 5 into the term formula, but my question is why did they list seemingly random numbers first... I had assumed that those were the 1st, 2nd, and 3rd terms, I tried to plug them in as recursive numbers. If someone could explain that would be fantastic Thanks guys! Happy studying and/or happy tutoring! Kali numbers are not random. plug in them to the formula n+2^n-1 so, ur 1st term will be equal to 1+2^1-1=1+1=2 (as it is mentioned in ur sequence) ur 2nd term is 2+2^2-12+2=4 ur 3d term is 3+2^3-1=3+4=7 the same sequence (2, 4, 7....) is listed in the q.stem hope it helps Newbie | Next Rank: 10 Posts Joined 06 Feb 2012 Posted: 3 messages Thanks Buddy Junior | Next Rank: 30 Posts Joined 18 Mar 2009 Posted: 16 messages kalifalk wrote: Hello all, I've never posted before, but I have a simple question about OG PS question #171. Question is: "What is the difference between the sixth and the fifth terms of the sequence 2, 4, 7.... whose nth term is n+2^n-1." According to the answer, you simply plug 6 and 5 into the term formula, but my question is why did they list seemingly random numbers first... I had assumed that those were the 1st, 2nd, and 3rd terms, I tried to plug them in as recursive numbers. If someone could explain that would be fantastic Thanks guys! Happy studying and/or happy tutoring! Kali The first term in the sequnce is n=0. So for the 5th term, n=4 and 6th term , n=5. Thus your answer comes to (4+2)^(4-1) which 6^3 and the 6th term should be (5+2)^(5-1) which is 7^4. Here, as you notice value of n is 1 less than the term of the sequnce (Eg: Sixth term is n=5). I feel this is the trick that they are testing. ### GMAT/MBA Expert GMAT Instructor Joined 09 Apr 2015 Posted: 1461 messages Followed by: 18 members Upvotes: 39 kalifalk wrote: Hello all, I've never posted before, but I have a simple question about OG PS question #171. Question is: "What is the difference between the sixth and the fifth terms of the sequence 2, 4, 7.... whose nth term is n+2^n-1." According to the answer, you simply plug 6 and 5 into the term formula, but my question is why did they list seemingly random numbers first... I had assumed that those were the 1st, 2nd, and 3rd terms, I tried to plug them in as recursive numbers. If someone could explain that would be fantastic Thanks guys! Happy studying and/or happy tutoring! Kali What is the difference between the sixth and the fifth terms of the sequence 2, 4, 7, ... whose nth term is n + 2^(n - 1)? (A) 2 (B) 3 (C) 6 (D) 16 (E) 17 Solution: To find the sixth term, let's first substitute 6 for n. 6 + 2^(6-1) 6 + 2^5 6 + 32 = 38 To find the fifth term, we substitute 5 for n. 5 + 2^(5-1) 5 + 2^4 5 + 16 = 21 The difference between the 6th and 5th terms of the sequence is 38 - 21 = 17. Answer: E ### GMAT/MBA Expert Elite Legendary Member Joined 23 Jun 2013 Posted: 10112 messages Followed by: 494 members Upvotes: 2867 GMAT Score: 800 Hi All, We're told that a sequence 2, 4, 7... is defined by the following: the Nth term is N + 2^(N - 1). We're asked for the the difference between the sixth and the fifth terms of the sequence. While sequence questions can sometimes look complex, they generally involve basic Arithmetic rules, so it can often help to figure out the first few terms of the sequence (so you understand how the sequence "works"). Here, the Nth term in the sequence can be determined with... N + 2^(N - 1) 1st term --> N = 1..... 1 + 2^(0) = 1+1 = 2 2nd term --> N = 2..... 2 + 2^(1) = 2+2 = 4 3rd term --> N = 3..... 3 + 2^(2) = 3+4 = 7 Etc. We're asked for the difference between the 6th and 5th terms... 5th term --> N = 5..... 5 + 2^(4) = 5+16 = 21 6th term --> N = 6..... 6 + 2^(5) = 6+32 = 38 38 - 21 = 17 Final Answer: E GMAT assassins aren't born, they're made, Rich • Free Practice Test & Review How would you score if you took the GMAT 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 • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • Free Trial & Practice Exam BEAT THE GMAT EXCLUSIVE 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 • Magoosh Study with Magoosh GMAT prep Available with Beat the GMAT members only code • Award-winning private GMAT tutoring Register now and save up to$200

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