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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 ## Mary is building a pyramid out of stacked rows of soup cans. tagged by: AAPL ##### This topic has 2 expert replies and 0 member replies ### Top Member ## Mary is building a pyramid out of stacked rows of soup cans. ## Timer 00:00 ## Your Answer A B C D E ## Global Stats Difficult Princeton Review Mary is building a pyramid out of stacked rows of soup cans. When completed, the top row of the pyramid contains a single soup can, and each row below the top row contains 6 more cans than the one above it. If the completed pyramid contains 16 rows, then how many soup cans did Mary use to build it? A. 91 B. 96 C. 728 D. 732 E. 736 OA E. ### GMAT/MBA Expert Elite Legendary Member Joined 23 Jun 2013 Posted: 10197 messages Followed by: 495 members Upvotes: 2867 GMAT Score: 800 Hi All, We're told that Mary is building a pyramid out of stacked rows of soup cans; the top row of the pyramid contains a single soup can, each row below the top row contains 6 MORE cans than the one above it and the completed pyramid contains 16 rows. We're asked for the TOTAL number of soup cans the pyramid. This question can be solved with a bit of Arithmetic and "bunching." To start, we can list out the first few terms in this sequence: 1, 7, 13, 19, 25...... each term increases by 6, so we can determine the 16th term (re: the last term) in the sequence 1 + (15)(6) = 1 + 90 = 91. Next, since the increase is a constant, we can 'bunch' the largest and smallest terms in the sequence and define a pattern: 1 + 91 = 92 7 + 85 = 92 13 + 79 = 92 Etc. We'll end up with 8 'pairs' of 92, so the total number of cans is (8)(92) = 736. Final Answer: E GMAT assassins aren't born, they're made, Rich _________________ Contact Rich at Rich.C@empowergmat.com ### GMAT/MBA Expert GMAT Instructor Joined 09 Oct 2010 Posted: 1449 messages Followed by: 32 members Upvotes: 59 AAPL wrote: Princeton Review Mary is building a pyramid out of stacked rows of soup cans. When completed, the top row of the pyramid contains a single soup can, and each row below the top row contains 6 more cans than the one above it. If the completed pyramid contains 16 rows, then how many soup cans did Mary use to build it? A. 91 B. 96 C. 728 D. 732 E. 736 OA E. $$?\,\,\, = \,\,\,\# \,\,{\rm{soup}}\,\,{\rm{cans}}$$ The number of soup cans constitute a finite arithmetic sequence, hence the average number of cans per row is equal to M = (1+N)/2 , where N is the number of cans in the 16th row, that is, 1+15*6 = 91. Hence: $$M = {{1 + 91} \over 2}\,\,\,\, \Rightarrow \,\,\,\,? = 16 \cdot \left( {{{1 + 91} \over 2}} \right) = 8 \cdot 92 = 736$$ This solution follows the notations and rationale taught in the GMATH method. Regards, Fabio. _________________ Fabio Skilnik :: GMATH method creator ( Math for the GMAT) English-speakers :: https://www.gmath.net Portuguese-speakers :: https://www.gmath.com.br • 5-Day Free Trial 5-day free, full-access trial TTP Quant 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 • Award-winning private GMAT tutoring Register now and save up to$200

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