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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 the 3rd term in a sequence tagged by: BTGmoderatorRO ##### This topic has 2 expert replies and 0 member replies ## If the 3rd term in a sequence If the 3rd term in a sequence is 25 and the 10th term is - 3. what is the 87th term in the sequence (A)15 (B)299 (C)-311 (D)- 354 (E)-408 OA is C Can an Expert help me with the formula here? Thanks ### GMAT/MBA Expert GMAT Instructor Joined 08 Dec 2008 Posted: 12418 messages Followed by: 1244 members Upvotes: 5254 GMAT Score: 770 Roland2rule wrote: If the 3rd term in a sequence is 25 and the 10th term is - 3. what is the 87th term in the sequence (A)15 (B)299 (C)-311 (D)- 354 (E)-408 OA is C Can an Expert help me with the formula here? Thanks This is not a GMAT-worthy question. What's the source? We have no information about this sequence to help us be certain of the value of the 87th term. In fact, the sequence COULD be as follows: 25, -3, 25, -3, 25, -3, 25, -3, 25, -3,.... [notice that the 3rd term is 25 and the 10th term is -3] In this case, the 87th term is 25 (not among the answer choices) Or, of course, the sequence could have a totally different pattern, in which case the answer is something else. Cheers, Brent _________________ Brent Hanneson â€“ Creator of GMATPrepNow.com Use our video course along with Sign up for our free Question of the Day emails And check out all of our free resources GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMATâ€™s FREE 60-Day Study Guide and reach your target score in 2 months! ### GMAT/MBA Expert GMAT Instructor Joined 09 Apr 2015 Posted: 1461 messages Followed by: 17 members Upvotes: 39 Roland2rule wrote: If the 3rd term in a sequence is 25 and the 10th term is - 3. what is the 87th term in the sequence (A)15 (B)299 (C)-311 (D)- 354 (E)-408 (Note: The problem doesnâ€™t say what kind of sequence it is, but letâ€™s assume that it is an arithmetic sequence since by looking at the answer choices, it seems to suggest the sequence is an arithmetic one.) Recall that the nth term, a_n, of an arithmetic sequence is given by the formula: a_n = a_1 + d(n - 1), where a_1 is the first term and d is the common difference. Another useful formula we can use (especially when two terms, a_m and a_k, are given) is: a_m = a_k + d(m - k). Since the 3rd term is 25 and the 10 term is -3, by letting m = 10 and k = 3, we can use the second formula to say: -3 = 25 + d(10 - 3) -28 = 7d -4 = d Use the second formula again, now letting m = 87 and k = 3 with d = -4, we have: a_87 = 25 + (-4)(87 - 3) a_ 87 = 25 - 336 a_87 = - 311 Answer: C _________________ Jeffrey Miller Head of GMAT Instruction • 5 Day FREE Trial Study Smarter, Not Harder Available with Beat the GMAT members only code • Magoosh Study with Magoosh GMAT prep 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 • 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 • Award-winning private GMAT tutoring Register now and save up to$200

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