|
|
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.
22 Jul 2013, 09:03
Kudos
Bookmarks
A
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
65%
(hard)
Question Stats:
57% (01:56) correct
43%
(01:54)
wrong
based on 347
sessions
History
Date
Time
Result
Not Attempted Yet
If x and y are integers such that x < y < 0 what is x?
(1) (x + y)(x - y) = 7
(2) xy = 12
Problem from GMAT Focus:
(1) (x + y)(x - y) = 7
(2) xy = 12
Problem from GMAT Focus:
Explanation for why A is the answer from GMAC goes something like this:
x^2-y^2=7
x^2=7+y^2
x=sqr root (7+y^2)
Then use trial and error to determine that y must be -3 and therefore x must be -4.
This doesn't make sense to me for the following reason:
If y=-3, then x=4 because a perfect square can never be negative... That's why I chose C as the answer instead.
Thoughts?
Thanks! I have never seen a problem like this before.
x^2-y^2=7
x^2=7+y^2
x=sqr root (7+y^2)
Then use trial and error to determine that y must be -3 and therefore x must be -4.
This doesn't make sense to me for the following reason:
If y=-3, then x=4 because a perfect square can never be negative... That's why I chose C as the answer instead.
Thoughts?
Thanks! I have never seen a problem like this before.
Pure algebraic questions like this one are no longer part of the GMAT Data Sufficiency syllabus.
For relevant Data Sufficiency questions, please check the Data Sufficiency forum:
Data Sufficiency Forum
Data Sufficiency Forum
22 Jul 2013, 09:11
Kudos
Bookmarks
If x and y are integers such that x<y<0 what is x?
(1) (x+y)(x-y)=7. x and y are integers means that both x+y and x-y are integers. So, we have that the product of two integer factors equal to 7. There are only two combination of such factors possible: (1, 7) and (-1, -7). Since given that x and y are both negative then the first case is out, so x-y is either -1 or -7, but it cannot be -7, because in this case x+y must be -1 and no sum of two negative integers yields -1. Hence x-y=-1 and x+y=-7. Solving gives x=-4 . Sufficient.
(2) xy=12. Clearly insufficient: consider (x, y)=(-12, -1) and (x, y)=(-4, -3).
Answer: A.
Hope it's clear.
(1) (x+y)(x-y)=7. x and y are integers means that both x+y and x-y are integers. So, we have that the product of two integer factors equal to 7. There are only two combination of such factors possible: (1, 7) and (-1, -7). Since given that x and y are both negative then the first case is out, so x-y is either -1 or -7, but it cannot be -7, because in this case x+y must be -1 and no sum of two negative integers yields -1. Hence x-y=-1 and x+y=-7. Solving gives x=-4 . Sufficient.
(2) xy=12. Clearly insufficient: consider (x, y)=(-12, -1) and (x, y)=(-4, -3).
Answer: A.
Hope it's clear.
