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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 ## sqrt(80) + tagged by: Brent@GMATPrepNow ##### This topic has 4 expert replies and 0 member replies ## sqrt(80) + ## Timer 00:00 ## Your Answer A B C D E ## Global Stats Difficult sqrt(80) + sqrt(125) = A) 9sqrt(5) B) 20sqrt(5) C) 41sqrt(5) D) sqrt(205) E) 100 OA: A ### GMAT/MBA Expert GMAT Instructor Joined 08 Dec 2008 Posted: 12744 messages Followed by: 1247 members Upvotes: 5254 GMAT Score: 770 boomgoesthegmat wrote: √80 + √125 = A) 9sqrt(5) B) 20sqrt(5) C) 41sqrt(5) D) sqrt(205) E) 100 OA: A IMPORTANT RULE: √(xy) = (√x)(√y) So, √80 + √125 = √(16 x 5) + √(25 x 5) = (√16)(√5) + (√25)(√5) = 4√5 + 5√5 = 9√5 = A Related Resource The following video covers the concepts/strategies that are useful for answering this question: - Simplifying roots: https://www.gmatprepnow.com/module/gmat-powers-and-roots/video/1038 Cheers, Brent _________________ Brent Hanneson – 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 GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months! ### GMAT/MBA Expert GMAT Instructor Joined 08 Dec 2008 Posted: 12744 messages Followed by: 1247 members Upvotes: 5254 GMAT Score: 770 boomgoesthegmat wrote: √80 + √125 = A) 9sqrt(5) B) 20sqrt(5) C) 41sqrt(5) D) sqrt(205) E) 100 OA: A Another approach is to ESTIMATE We know that √81 = 9, so √80 is a little bit less than 9 We know that √121 = 11, so √125 is a little bit more than 11 So, √80 + √125 ≈ 9 + 11 ≈ 20 When we check the answer choices, we must keep in mind that √5 ≈ 2.2 A) 9√5 ≈ (9)(2.2) ≈ 20 NICE!! B) 20√5 ≈ (20)(2.2) ≈ 44 NO GOOD. ELIMINATE C) 41√5 ≈ (20)(2.2) ≈ TOO BIG. ELIMINATE D) √205. We know that √225 = 15. So, √205 is too small. ELIMINATE E) 100 ELIMINATE Answer: B Cheers, Brent _________________ Brent Hanneson – 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 GMAT’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: 18 members Upvotes: 39 boomgoesthegmat wrote: sqrt(80) + sqrt(125) = A) 9sqrt(5) B) 20sqrt(5) C) 41sqrt(5) D) sqrt(205) E) 100 √80 = √16 x √5 = 4√5 √125 = √25 x √5 = 5√5 Now we can add these two results together: 4√5 + 5√5 = 9√5 Answer: A _________________ Jeffrey Miller Head of GMAT Instruction ### 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 asked for the value of √80 + √125. This question comes down to some standard Radical rules (which you will likely be asked to use 1-2 times on Test Day). You likely already know a number of perfect squares already (1, 4, 9, 16, 25, etc.), so you can square-root each of those numbers too. When a prompt gives you a radical that is NOT a perfect square, a good 'first step' is often to try to break that radical into 'pieces' (with one of the pieces being a perfect square). With √80, we can rewrite that value as √(5)(16)... and then 'pull out' the 16, giving us 4√5 We can do the same thing with the √125.... √(5)(25)... and then 'pull out' the 25, giving us 5√5 Thus, the sum of those two values is... 4√5 + 5√5 = 9√5 Final Answer: A GMAT assassins aren't born, they're made, Rich _________________ Contact Rich at Rich.C@empowergmat.com • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • FREE GMAT Exam Know how you'd score today for$0

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