November 17, 2018 November 17, 2018 07:00 AM PST 09:00 AM PST Nov. 17, 7 AM PST. Aiming to score 760+? Attend this FREE session to learn how to Define your GMAT Strategy, Create your Study Plan and Master the Core Skills to excel on the GMAT. November 17, 2018 November 17, 2018 09:00 AM PST 11:00 AM PST Join the Quiz Saturday November 17th, 9 AM PST. The Quiz will last approximately 2 hours. Make sure you are on time or you will be at a disadvantage.
Author 
Message 
TAGS:

Hide Tags

Intern
Joined: 17 Feb 2015
Posts: 3
Concentration: Strategy, Strategy
GPA: 3.8
WE: Engineering (Energy and Utilities)

Re: Math Revolution and GMAT Club Contest! x + y = ?
[#permalink]
Show Tags
17 Dec 2015, 20:58
x + y = ? (1) y=2x−1 (2) y^2=−1−2x
As this is a two variable equation with two unknowns there should be two equations to solve it. From eq1 alone we cant find x+y so using eq2 we should see wether x+y can be found or not From eq2 for x<1/2 12x is positive so y^2=2x1 this happens only when y=y^2 so Y=1 => X=1 for x>1/2 Y^2=12X and Y=2x1 this happens when Y=1 => X=0 for x=1/2 Y=0 so, by using the above two conditions we can determine x+y



Moderator
Joined: 21 Jun 2014
Posts: 1053
Location: India
Concentration: General Management, Technology
GPA: 2.49
WE: Information Technology (Computer Software)

Re: Math Revolution and GMAT Club Contest! x + y = ?
[#permalink]
Show Tags
19 Dec 2015, 01:57
x+y = ?1) y = 2x 1 clearly INSUFFICIENT. two unknown one equation. for x = 0, y = 1 for x = 1/2, y = 0 for x = 1, y = 1 2) y^2 =  12x y^2 + 12x = 0, As we know that square of a number is always +ve and absolute value is always positive too. sum of two +ve entities can be zero only when their individual value is zero Hence, y = 0 and 12x will only be zero when x = 1/2 x+y = 1/2+0 = 1/2  definite, SUFFICIENT. Option B is the correct answer.
_________________
 Target  720740 Project PS Butler  https://gmatclub.com/forum/projectpsbutlerpracticeeveryday280904.html http://gmatclub.com/forum/informationonnewgmatesrreportbeta221111.html http://gmatclub.com/forum/listofoneyearfulltimembaprograms222103.html



Intern
Joined: 05 Jun 2013
Posts: 35

Re: Math Revolution and GMAT Club Contest! x + y = ?
[#permalink]
Show Tags
19 Dec 2015, 03:30
x + y = ?
Taking choice 1 (1) y=2x−1 x, y can be anything. When x =0, y=1 or when x=1,y=1. Therefore this choice is not sufficient.
(2) y2=−1−2x
x, y can be anything. When x =1, y= (3^0.5) or when x=1/2,y=0. Therefore this choice is not sufficient.
Combining choice 1 and choice 2. y=2x−1 , y2=−1−2x Squaring choice 1. y^2 = (2x1)^2 and substituting in choice 2 in place of y^2. (2x1)^2 =  12x
12x can also be written as (12x)^2 which can also be written as ((1)(2x1))^2 which is (2x1)^2. Therefore (2x1)^2 =  (2x1)^2 (2x1)^2 + (2x1)^2 =0 2((2x1)^2)=0 x=1/2. Substituting x value in choice 1 y=2x1 gives y=0. Therefore x+y= 1/2. So, both statements (1) and (2) TOGETHER are sufficient to answer the question and answer choice C.



Intern
Joined: 09 Sep 2015
Posts: 32

Re: Math Revolution and GMAT Club Contest! x + y = ?
[#permalink]
Show Tags
19 Dec 2015, 04:49
x+y =?
1) y=2x1 so x+y x+2x1 3x1 (ns)
2) y^2=12x
as LHS will be positive always..
so RHS has to be positive
so, y^2 = (12x) y^2 = 2x1 (NS)
1+2
Y=2X1 Y^2= 2X1 (2x1)^2 = (2x1) x=1/2, 1 y=0,1 so ans, E



Math Expert
Joined: 02 Sep 2009
Posts: 50619

Re: Math Revolution and GMAT Club Contest! x + y = ?
[#permalink]
Show Tags
20 Dec 2015, 09:40
Bunuel wrote: Math Revolution and GMAT Club Contest Starts! QUESTION #9:x + y = ? (1) \(y = 2x  1\) (2) \(y^2 = 1  2x\) Check conditions below: Math Revolution and GMAT Club ContestThe Contest Starts November 28th in Quant Forum We are happy to announce a Math Revolution and GMAT Club Contest For the following four (!) weekends we'll be publishing 4 FRESH math questions per weekend (2 on Saturday and 2 on Sunday). To participate, you will have to reply with your best answer/solution to the new questions that will be posted on Saturday and Sunday at 9 AM Pacific. Then a week later, the forum moderator will be selecting 2 winners who provided most correct answers to the questions, along with best solutions. Those winners will get 6months access to GMAT Club Tests. PLUS! Based on the answers and solutions for all the questions published during the project ONE user will be awarded with ONE Grand prize: PS + DS course with 502 videos that is worth $299! All announcements and winnings are final and no whining GMAT Club reserves the rights to modify the terms of this offer at any time. NOTE: Test Prep Experts and Tutors are asked not to participate. We would like to have the members maximize their learning and problem solving process.
Thank you! MATH REVOLUTION OFFICIAL SOLUTION:Since we have 2 variables in the original condition, we also need 2 equations. Since we need both 1) and 2), the correct answer is likely C. Using con 1) & 2) together, we get x=1/2, y=0. This is unique and sufficient. Therefore, the correct answer is C. However, since this is an “absolute value” problem, which is one of the key questions, we should apply Common Mistake Type 4(A). In case of con 1), the values of x, y are not unique. Therefore, it is not sufficient. In case of con 2), the only values that satisfy y^2+12x=0 are x=1/2, y=0. Therefore, it is unique and sufficient. The correct answer is B. If C and B are both correct answers, B is would be the final correct answer. Note 1 : a=b=0 is required to satisfy a+b=0 or a2+b2=0. Also, solving this type of question usually takes over 5 minutes during the actual exam. However, if you understand the relationship between Variable Approach Method and Common Mistake Types, you will be able to solve this type of question in just about 2 minutes. Note 2 : For cases where we need 2 more equations, such as original conditions with “2 variables”, or “3 variables and 1 equation”, or “4 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 70% chance that C is the answer, while E has 25% chance. These two are the majority. In case of common mistake type 3,4, the answer may be from A, B or D but there is only 5% chance. Since C is most likely to be the answer using 1) and 2) separately according to DS definition (It saves us time). Obviously there may be cases where the answer is A, B, D or E.
_________________
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: 05 Jun 2013
Posts: 35

Re: Math Revolution and GMAT Club Contest! x + y = ?
[#permalink]
Show Tags
25 Dec 2015, 06:46
x + y = ?
(1) y=2x−1 (2) y2=−1−2x
I have a doubt. Here no information about x and y are given as they are integers. Is it correct to assume that y2=−1−2x , here y^2 cannot be a negative number and therefore y^2= 0 and mark B as sufficient. Can't y be a complex number as no information is given that y is integer?
y2 =  negative number I assumed that y = complex number and marked choice B as insufficient since y can be any complex number based on x, in my above answer.
MathExperts! Can you please help clear my doubt. Is it wrong to assume in GMAT , that a number can be complex number if no information is given about it.



Math Expert
Joined: 02 Sep 2009
Posts: 50619

Re: Math Revolution and GMAT Club Contest! x + y = ?
[#permalink]
Show Tags
27 Dec 2015, 03:52
sri1sastra wrote: x + y = ?
(1) y=2x−1 (2) y2=−1−2x
I have a doubt. Here no information about x and y are given as they are integers. Is it correct to assume that y2=−1−2x , here y^2 cannot be a negative number and therefore y^2= 0 and mark B as sufficient. Can't y be a complex number as no information is given that y is integer?
y2 =  negative number I assumed that y = complex number and marked choice B as insufficient since y can be any complex number based on x, in my above answer.
MathExperts! Can you please help clear my doubt. Is it wrong to assume in GMAT , that a number can be complex number if no information is given about it. All numbers on the GMAT are by default real numbers. So, we do not consider complex/imaginary numbers on the GMAT.
_________________
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: 8791

Re: Math Revolution and GMAT Club Contest! x + y = ?
[#permalink]
Show Tags
19 Jul 2018, 15:26
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: Math Revolution and GMAT Club Contest! x + y = ? &nbs
[#permalink]
19 Jul 2018, 15:26



Go to page
Previous
1 2
[ 28 posts ]



