• 7 CATs FREE!
If you earn 100 Forum Points

Engage in the Beat The GMAT forums to earn
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 x and y are positive numbers and z = xy^2, a 50 percent.. tagged by: BTGmoderatorLU ##### This topic has 2 expert replies and 0 member replies ### Top Member ## If x and y are positive numbers and z = xy^2, a 50 percent.. If x and y are positive numbers and z = xy^2, a 50 percent increase in x and 20 percent decrease in y would result in which of the following changes in z? A) A decrease of 4% B) A decrease of 14% C) An increase of 4% D) An increase of 20% E) An increase of 30% The OA is A. If x increase by 50% then, x = 1.5x If y decrease by 20% then, y = 0.8y Finally, z = (1.5x)(0.8y)^2 = 0.96xy^2, that's represent a decrease of 4% in z, right? Experts, any suggestion? Thanks in advance. ### GMAT/MBA Expert GMAT Instructor Joined 25 May 2010 Posted: 14940 messages Followed by: 1855 members Upvotes: 13060 GMAT Score: 790 LUANDATO wrote: If x and y are positive numbers and z = xy^2, a 50 percent increase in x and 20 percent decrease in y would result in which of the following changes in z? A) A decrease of 4% B) A decrease of 14% C) An increase of 4% D) An increase of 20% E) An increase of 30% Since x increases by 50% = 1/2, plug in an EVEN NUMBER for x: x=4. Since y decreases by 20% = 1/5, plug in a MULTIPLE OF 5 for y: y=5. Original z: z = xyÂ² = (4)(5Â²) = 4*25 = 100. New z: x increased by 1/2 = 4 + (1/2)(4) = 4 + 2 = 6. y decreased by 1/5 = 5 - (1/5)(5) = 5 - 1 = 4. z = xyÂ² = (6)(4Â²) = 6*16 = 96. Result: z decreases from 100 to 96, a decrease of 4%. The correct answer is A. Quote: If x increase by 50% then, x = 1.5x If y decrease by 20% then, y = 0.8y Finally, z = (1.5x)(0.8y)^2 = 0.96xy^2, that's represent a decrease of 4% in z, right Perfect! _________________ Mitch Hunt Private Tutor for the GMAT and GRE GMATGuruNY@gmail.com If you find one of my posts helpful, please take a moment to click on the "UPVOTE" icon. Available for tutoring in NYC and long-distance. For more information, please email me at GMATGuruNY@gmail.com. Student Review #1 Student Review #2 Student Review #3 Free GMAT Practice Test How can you improve your test score if you don't know your baseline score? Take a free online practice exam. Get started on achieving your dream score today! Sign up now. ### GMAT/MBA Expert GMAT Instructor Joined 09 Apr 2015 Posted: 1461 messages Followed by: 17 members Upvotes: 39 LUANDATO wrote: If x and y are positive numbers and z = xy^2, a 50 percent increase in x and 20 percent decrease in y would result in which of the following changes in z? A) A decrease of 4% B) A decrease of 14% C) An increase of 4% D) An increase of 20% E) An increase of 30% Since x increases by 50% and y decreases by 20% we have: z = (1.5x)(0.8y)^2 z = (1.5x)0.64y^2 z = 0.96xy^2 So we see that z is decreased by 4%. Alternate Solution: If we let x = 1 and y = 1, then the initial value of z is also 1. After we increase x by 50% and decrease y by 20%, we have: z = 1.5*(0.8)^2 z = 0.96 We use the percent change formula (new - old)/old x 100% to get: (0.96 - 1)/1 x 100% = -0.04 x 100% = 4% decrease. Answer: A _________________ Jeffrey Miller Head of GMAT Instruction • 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 • 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 • 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

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

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

### Top First Responders*

1 Brent@GMATPrepNow 64 first replies
2 fskilnik@GMATH 58 first replies
3 Jay@ManhattanReview 46 first replies
4 GMATGuruNY 34 first replies
5 Rich.C@EMPOWERgma... 24 first replies
* Only counts replies to topics started in last 30 days
See More Top Beat The GMAT Members

### Most Active Experts

1 fskilnik@GMATH

GMATH Teacher

120 posts
2 Brent@GMATPrepNow

GMAT Prep Now Teacher

99 posts
3 Max@Math Revolution

Math Revolution

88 posts
4 Jay@ManhattanReview

Manhattan Review

82 posts
5 Rich.C@EMPOWERgma...

EMPOWERgmat

65 posts
See More Top Beat The GMAT Experts