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# If xy=4, x/y=36, for positive numbers x and y, y=?

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 9014
GMAT 1: 760 Q51 V42
GPA: 3.82
If xy=4, x/y=36, for positive numbers x and y, y=?  [#permalink]

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27 Jun 2016, 17:41
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5% (low)

Question Stats:

92% (01:21) correct 8% (01:38) wrong based on 150 sessions

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If xy=4, x/y=36, for positive numbers x and y, y=?
A. 1/2
B. 2
C. 1/3
D. 3
E. 1/6

*Answer will be posted in 2 days.

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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
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"Only $79 for 1 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Manager Joined: 22 Jun 2016 Posts: 223 Re: If xy=4, x/y=36, for positive numbers x and y, y=? [#permalink] ### Show Tags 27 Jun 2016, 20:51 Very easy question. 2 variables and 2 easy equations. xy=4 ---> x=4/y - (i) x/y=36 ---> replacing (i) here ---> 4/(y^2)=36 ---> y^2=4/36=1/9 ---> y=1/3 or -1/3 The question states that x and y are positive integers. Therefore, y=1/3 is the answer. Answer C. ------------------------------------------- P.S. Don't forget to give Kudos Board of Directors Status: QA & VA Forum Moderator Joined: 11 Jun 2011 Posts: 4996 Location: India GPA: 3.5 WE: Business Development (Commercial Banking) Re: If xy=4, x/y=36, for positive numbers x and y, y=? [#permalink] ### Show Tags 28 Jun 2016, 10:08 MathRevolution wrote: If xy=4, x/y=36, for positive numbers x and y, y=? A. 1/2 B. 2 C. 1/3 D. 3 E. 1/6 *Answer will be posted in 2 days. $$\frac{x}{y}$$=36 So, x = 36y Now, It is given ; xy=4 Or, $$(36y)y$$ = 4 Or, $$(y^2 )6^2$$ = $$2^2$$ Or, 6y = 2 Or, y = $$\frac{1}{3}$$ Hence answer will be (C) _________________ Thanks and Regards Abhishek.... PLEASE FOLLOW THE RULES FOR POSTING IN QA AND VA FORUM AND USE SEARCH FUNCTION BEFORE POSTING NEW QUESTIONS How to use Search Function in GMAT Club | Rules for Posting in QA forum | Writing Mathematical Formulas |Rules for Posting in VA forum | Request Expert's Reply ( VA Forum Only ) GMAT Club Legend Joined: 11 Sep 2015 Posts: 4881 Location: Canada GMAT 1: 770 Q49 V46 Re: If xy=4, x/y=36, for positive numbers x and y, y=? [#permalink] ### Show Tags 28 Jun 2016, 11:43 Top Contributor MathRevolution wrote: If xy=4, x/y=36, for positive numbers x and y, y=? A. 1/2 B. 2 C. 1/3 D. 3 E. 1/6 Another approach is to check the answer choices. A) y = 1/2 Since xy = 4, we can conclude that x = 8 If y = 1/2 and x = 8, then x/y = (8)/(1/2) = 16. NOT GOOD, x/y is SUPPOSED to equal 36 ELIMINATE A B) y = 2 Since xy = 4, we can conclude that x = 2 If y = 2 and x = 2, then x/y = 2/2 = 1. NOT GOOD, x/y is SUPPOSED to equal 36 ELIMINATE B C) y = 1/3 Since xy = 4, we can conclude that x = 12 If y = 1/3 and x = 12, then x/y = (12)/(1/3) = 36. GREAT! x/y is SUPPOSED to equal 36 Answer: _________________ Test confidently with gmatprepnow.com VP Joined: 07 Dec 2014 Posts: 1252 Re: If xy=4, x/y=36, for positive numbers x and y, y=? [#permalink] ### Show Tags 28 Jun 2016, 15:04 (x/y)/xy=36/4 y^2=1/9 y=1/3 GMAT Club Legend Joined: 11 Sep 2015 Posts: 4881 Location: Canada GMAT 1: 770 Q49 V46 Re: If xy=4, x/y=36, for positive numbers x and y, y=? [#permalink] ### Show Tags 28 Jun 2016, 15:05 Top Contributor gracie wrote: (x/y)/xy=36/4 y^2=1/9 y=1/3 Nice! I love the different ways these kinds of questions can be solved. _________________ Test confidently with gmatprepnow.com Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 9014 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: If xy=4, x/y=36, for positive numbers x and y, y=? [#permalink] ### Show Tags 29 Jun 2016, 19:13 If we substitute in x=4/y, from 4/y^2 =36, we get y^2=1/9. Hence, y=1/3. Thus, the correct answer is C. _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$79 for 1 month Online Course"
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Re: If xy=4, x/y=36, for positive numbers x and y, y=?   [#permalink] 29 Jun 2016, 19:13