December 17, 2018 December 17, 2018 06:00 PM PST 07:00 PM PST Join our live webinar and learn how to approach Data Sufficiency and Critical Reasoning problems, how to identify the best way to solve each question and what most people do wrong. December 16, 2018 December 16, 2018 07:00 AM PST 09:00 AM PST Get personalized insights on how to achieve your Target Quant Score.
Author 
Message 
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 51229

Bank account A contains exactly x dollars, an amount that will decreas
[#permalink]
Show Tags
12 Jun 2015, 02:49
Question Stats:
76% (02:12) correct 24% (02:26) wrong based on 223 sessions
HideShow timer Statistics



CEO
Status: GMATINSIGHT Tutor
Joined: 08 Jul 2010
Posts: 2711
Location: India
GMAT: INSIGHT
WE: Education (Education)

Bank account A contains exactly x dollars, an amount that will decreas
[#permalink]
Show Tags
12 Jun 2015, 03:19
Bunuel wrote: Bank account A contains exactly x dollars, an amount that will decrease by 10% each month for the next two months. Bank account B contains exactly y dollars, an amount that will increase by 20% each month for the next two months. If A and B contain the same amount at the end of two months, what is the ratio of \(\sqrt{x}\) to \(\sqrt{y}\)?
(A) 4 : 3 (B) 3 : 2 (C) 16 : 9 (D) 2 : 1 (E) 9 : 4
Kudos for a correct solution. Initial Amount Bank A $x Bank B $y Aft. 1st Month $0.9*x $1.2*y Aft. 1st Month $0.9^2*x $1.2^2*y Now, 0.9^2*x = 1.2^2*y i.e. 0.81x = 1.44y i.e. x/y = 1.44/0.81 i.e. \(\sqrt{x}/\sqrt{y} = \sqrt{1.44}/\sqrt{0.81}\) i.e. \(\sqrt{x}/\sqrt{y} = 12/9 = 4/3\) Answer: Option
_________________
Prosper!!! GMATinsight Bhoopendra Singh and Dr.Sushma Jha email: info@GMATinsight.com I Call us : +919999687183 / 9891333772 Online OneonOne Skype based classes and Classroom Coaching in South and West Delhi http://www.GMATinsight.com/testimonials.html
ACCESS FREE GMAT TESTS HERE:22 ONLINE FREE (FULL LENGTH) GMAT CAT (PRACTICE TESTS) LINK COLLECTION



Intern
Joined: 03 Feb 2015
Posts: 8
Concentration: Entrepreneurship, Finance
GPA: 3.59

Re: Bank account A contains exactly x dollars, an amount that will decreas
[#permalink]
Show Tags
12 Jun 2015, 04:58
Bunuel wrote: Bank account A contains exactly x dollars, an amount that will decrease by 10% each month for the next two months. Bank account B contains exactly y dollars, an amount that will increase by 20% each month for the next two months. If A and B contain the same amount at the end of two months, what is the ratio of \(\sqrt{x}\) to \(\sqrt{y}\)?
(A) 4 : 3 (B) 3 : 2 (C) 16 : 9 (D) 2 : 1 (E) 9 : 4
Kudos for a correct solution. For bank account A. you get the amount 90 (1st month after 10% decrease) and then 909(10% of 90) in 2nd month. Total 81 For bank account B. you get 120 (1st month 20% increase) and then 120+24 (2nd month: 20% increase on 120). Total 144 both contain the same amount after 2 months so: 81X = 144Y (Keep it simple by not using X and Y in the beginning) X/Y = 144/81 \(\sqrt{X}/\sqrt{Y} = \sqrt{144} / \sqrt{81}\) \(\sqrt{X}/\sqrt{Y} = 12/9 = 4/3\)



Manager
Joined: 26 Dec 2011
Posts: 114

Re: Bank account A contains exactly x dollars, an amount that will decreas
[#permalink]
Show Tags
12 Jun 2015, 05:00
Bank account A contains exactly x dollars, an amount that will decrease by 10% each month for the next two months. Bank account B contains exactly y dollars, an amount that will increase by 20% each month for the next two months. If A and B contain the same amount at the end of two months, what is the ratio of x√ to y√? (A) 4 : 3 (B) 3 : 2 (C) 16 : 9 (D) 2 : 1 (E) 9 : 4 Explanation: Account A has amount after 2 months = 0.9*0.9*x = 0.81*x Account B has amount after 2 months = 1.2*1.2*y = 1.44*y 0.81*x=1.44*y > √(x/y)=√(1.44/0.81) = 12/9 = 4/3. Ans A Thanks Please give me Kudos
_________________
Thanks, Kudos Please



Intern
Joined: 08 Jun 2015
Posts: 3

Re: Bank account A contains exactly x dollars, an amount that will decreas
[#permalink]
Show Tags
13 Jun 2015, 13:46
Bunuel wrote: Bank account A contains exactly x dollars, an amount that will decrease by 10% each month for the next two months. Bank account B contains exactly y dollars, an amount that will increase by 20% each month for the next two months. If A and B contain the same amount at the end of two months, what is the ratio of \(\sqrt{x}\) to \(\sqrt{y}\)?
(A) 4 : 3 (B) 3 : 2 (C) 16 : 9 (D) 2 : 1 (E) 9 : 4
Kudos for a correct solution. Hello, using smart numbers  applied the percentage discount or premium for each bank. Starting with the ratio in A calculate the % increase after 2 months and so forth until you get a ratio where both banks end with the same dollar amount use a multiplier of 10 so we're working with numbers easily multiplied by 10% (A) 4:3 => 40:30 = 40*.9=36*.9=$32.40 @ end of 2 months 30*1.20=36 you can stop and cross this off because the amount increase will exceed the end amount for bank A (B) 3:2 => 30:20 = 30*.9=27*.9=$24.30 @ end of 2 months 20*1.20=24 as with answer (A) you can stop and cross this off because the amount is close to the end amount for bank A (c) 16:9 => 160:90 = 160*.9 =144*.9=$129.60 @ end of 2 months 90*1.20=108*1.20=$129.60 match! the answer is (C) 16:9



EMPOWERgmat Instructor
Status: GMAT Assassin/CoFounder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 13099
Location: United States (CA)

Re: Bank account A contains exactly x dollars, an amount that will decreas
[#permalink]
Show Tags
13 Jun 2015, 15:00
Hi AnniK, Your approach to TEST VALUES would absolutely work on this question. However, there is an error in your work: Since the question asks for the ratio of √X to √Y, but the prompt asks us to 'manipulate' X and Y, you actually have to SQUARE the answer choices BEFORE you TEST VALUES. Your TESTs assume that the given answer choices are referring to X and Y, when they actually refer to √X and √Y. GMAT assassins aren't born, they're made, Rich
_________________
760+: Learn What GMAT Assassins Do to Score at the Highest Levels Contact Rich at: Rich.C@empowergmat.com
Rich Cohen
CoFounder & GMAT Assassin
Special Offer: Save $75 + GMAT Club Tests Free
Official GMAT Exam Packs + 70 Pt. Improvement Guarantee www.empowergmat.com/
*****Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!*****



Intern
Joined: 08 Jun 2015
Posts: 3

Re: Bank account A contains exactly x dollars, an amount that will decreas
[#permalink]
Show Tags
13 Jun 2015, 18:26
Hi EMPOWERgmatRichC/Rich,
Thank you for the explanation, I was thinking about that after submitting the response, guess the 'gut feeling' was correct.
Much appreciated
A



Senior Manager
Status: Math is psychological
Joined: 07 Apr 2014
Posts: 417
Location: Netherlands
GMAT Date: 02112015
WE: Psychology and Counseling (Other)

Bank account A contains exactly x dollars, an amount that will decreas
[#permalink]
Show Tags
14 Jun 2015, 03:40
Yep, I also found 4:3, working the problem like this: .........................................A..........................................B Now..................................x...........................................y +1 month.....................x(0.1x).....................................y+(0.2y) +2 months...............x(0.1x)  0.1 [x(0.1x)]..........y+(0.2y) + 0.2[y+(0.2y)]
Now we equate the 2 final amounts, as they need to be equal: x(0.1x)  0.1 [x(0.1x)] = y+(0.2y) + 0.2[y+(0.2y)] 0.81x = 1.44y 81x=144y x/y = 144/81 and their √ are x/y = 4/3. So, ANS A



Manager
Joined: 01 Jan 2015
Posts: 56

Re: Bank account A contains exactly x dollars, an amount that will decreas
[#permalink]
Show Tags
14 Jun 2015, 08:49
account A after 2 months = 0.9x0.9xx = 0.81x account B after 2 months = 1.2x1.2xy = 1.44y 0.81x=1.44y = root(x/y)=root(1.44/0.81) = 12/9 = 4/3.
Answer A



Math Expert
Joined: 02 Sep 2009
Posts: 51229

Re: Bank account A contains exactly x dollars, an amount that will decreas
[#permalink]
Show Tags
15 Jun 2015, 03:22
Bunuel wrote: Bank account A contains exactly x dollars, an amount that will decrease by 10% each month for the next two months. Bank account B contains exactly y dollars, an amount that will increase by 20% each month for the next two months. If A and B contain the same amount at the end of two months, what is the ratio of \(\sqrt{x}\) to \(\sqrt{y}\)?
(A) 4 : 3 (B) 3 : 2 (C) 16 : 9 (D) 2 : 1 (E) 9 : 4
Kudos for a correct solution. MANHATTAN GMAT OFFICIAL SOLUTION:First, note the answer pairs (A)&(C) and (B)&(E), in which one ratio is the square of the other. This represents a likely trap in a problem that asks for the ratio of \(\sqrt{x}\) to \(\sqrt{y}\) to rather than the more typical ratio of x to y. We can eliminate (D), as it is not paired with a trap answer and therefore probably not the correct answer. We should also suspect that the correct answer is (A) or (B), the “square root” answer choice in their respective pairs. For problems involving successive changes in amounts — such as populationgrowth problems, or compound interest problems — it is helpful to make a table: Attachment:
20150615_1512.png [ 51.28 KiB  Viewed 2341 times ]
If the accounts have the same amount of money after two months, then: 81/100*x = 144/100*y; x/y = 144/81; \(\frac{\sqrt{x}}{\sqrt{y}} = \frac{12}{9}\). The correct answer is A.
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Intern
Joined: 14 Mar 2015
Posts: 17
Location: India
Concentration: General Management, Strategy
GPA: 3.53
WE: Engineering (Other)

Bank account A contains exactly x dollars, an amount that will decreas
[#permalink]
Show Tags
12 Jul 2015, 18:24
Thanks Bunuel! I liked the strategy to eliminate wrong answers. I usually start solving problem without looking at answers. Does paying attention to answer choices reduce time required to solve question? Bunuel wrote: Bunuel wrote: Bank account A contains exactly x dollars, an amount that will decrease by 10% each month for the next two months. Bank account B contains exactly y dollars, an amount that will increase by 20% each month for the next two months. If A and B contain the same amount at the end of two months, what is the ratio of \(\sqrt{x}\) to \(\sqrt{y}\)?
(A) 4 : 3 (B) 3 : 2 (C) 16 : 9 (D) 2 : 1 (E) 9 : 4
Kudos for a correct solution. MANHATTAN GMAT OFFICIAL SOLUTION:First, note the answer pairs (A)&(C) and (B)&(E), in which one ratio is the square of the other. This represents a likely trap in a problem that asks for the ratio of \(\sqrt{x}\) to \(\sqrt{y}\) to rather than the more typical ratio of x to y. We can eliminate (D), as it is not paired with a trap answer and therefore probably not the correct answer. We should also suspect that the correct answer is (A) or (B), the “square root” answer choice in their respective pairs. For problems involving successive changes in amounts — such as populationgrowth problems, or compound interest problems — it is helpful to make a table: Attachment: 20150615_1512.png If the accounts have the same amount of money after two months, then: 81/100*x = 144/100*y; x/y = 144/81; \(\frac{\sqrt{x}}{\sqrt{y}} = \frac{12}{9}\). The correct answer is A.



Math Expert
Joined: 02 Sep 2009
Posts: 51229

Re: Bank account A contains exactly x dollars, an amount that will decreas
[#permalink]
Show Tags
13 Jul 2015, 00:05
123mba123 wrote: Thanks Bunuel! I liked the strategy to eliminate wrong answers. I usually start solving problem without looking at answers. Does paying attention to answer choices reduce time required to solve question? Bunuel wrote: Bunuel wrote: Bank account A contains exactly x dollars, an amount that will decrease by 10% each month for the next two months. Bank account B contains exactly y dollars, an amount that will increase by 20% each month for the next two months. If A and B contain the same amount at the end of two months, what is the ratio of \(\sqrt{x}\) to \(\sqrt{y}\)?
(A) 4 : 3 (B) 3 : 2 (C) 16 : 9 (D) 2 : 1 (E) 9 : 4
Kudos for a correct solution. MANHATTAN GMAT OFFICIAL SOLUTION:First, note the answer pairs (A)&(C) and (B)&(E), in which one ratio is the square of the other. This represents a likely trap in a problem that asks for the ratio of \(\sqrt{x}\) to \(\sqrt{y}\) to rather than the more typical ratio of x to y. We can eliminate (D), as it is not paired with a trap answer and therefore probably not the correct answer. We should also suspect that the correct answer is (A) or (B), the “square root” answer choice in their respective pairs. For problems involving successive changes in amounts — such as populationgrowth problems, or compound interest problems — it is helpful to make a table: Attachment: 20150615_1512.png If the accounts have the same amount of money after two months, then: 81/100*x = 144/100*y; x/y = 144/81; \(\frac{\sqrt{x}}{\sqrt{y}} = \frac{12}{9}\). The correct answer is A.Yes, on the PS section always look at the answer choices before you start to solve a problem. They might often give you a clue on how to approach the question.
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



NonHuman User
Joined: 09 Sep 2013
Posts: 9192

Re: Bank account A contains exactly x dollars, an amount that will decreas
[#permalink]
Show Tags
31 Dec 2017, 08:52
Hello from the GMAT Club BumpBot! Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up  doing my job. I think you may find it valuable (esp those replies with Kudos). Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
GMAT Books  GMAT Club Tests  Best Prices on GMAT Courses  GMAT Mobile App  Math Resources  Verbal Resources




Re: Bank account A contains exactly x dollars, an amount that will decreas &nbs
[#permalink]
31 Dec 2017, 08:52






