Events & Promotions
|
|
GMAT Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.
Customized
for You
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Apr 2808:00 AM PDT
-11:00 AM PDT
Whether you are just beginning your MBA journey or fine-tuning your path to a 700+ score, GMAT Day is designed to give you a competitive edge.
15 Dec 2012, 11:33
Kudos
Bookmarks
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
25%
(medium)
Question Stats:
74% (01:10) correct
26%
(01:10)
wrong
based on 323
sessions
History
Date
Time
Result
Not Attempted Yet
What is the value of y?
(1) x^2 - y^2 = 5
(2) x and y are each positive integers
(1) x^2 - y^2 = 5
(2) x and y are each positive integers
16 Dec 2012, 08:06
Kudos
Bookmarks
mridulparashar1
The red part is not correct. From x^2 - y^2 = 5 we cannot say that x-y=1 and x+y=5 (or vise-versa) because for (1) we don't know whether x and y are integers. So, for example it's possible that x-y=10 and x+y=1/2. Even if we knew that x and y are integers, still from (x+y)(x-y)=5 it follows that x+y=5 and x-y=1 (or vise versa) OR x+y=-5 and x-y=-1 (or vise versa).
What is the value of y?
(1) x^2 - y^2 = 5. Infinitely many solutions exist for x and y. Not sufficient.
(2) x and y are each positive integers. Not sufficient.
(1)+(2) Since \(x\) and \(y\) are positive integers then \(x+y=integer>0\) and \(x-y=integer\) AND \(x+y>x-y\). Thus from \(x^2 - y^2 =(x+y)(x-y)= 5\) we'd have that \(x+y=5\) and \(x-y=1\), from which it follows that \(y=2\). Sufficient.
Answer: C.
General Discussion
16 Dec 2012, 02:52
Kudos
Bookmarks
JJ2014
Hi,
From 1, we get (x-y)(x+y)=5 i.e (x-y)=1,5 or (x+y)= 5,1...solving we get 2 values of y (one positive and one negative)
From 2 alone we get nothing
combining 1 & 2 we get X and Y as postive and we get one solution
