GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 19 Sep 2018, 19:54

### 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

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# What is the value of (x - y)^4?

Author Message
TAGS:

### Hide Tags

Intern
Joined: 20 Feb 2012
Posts: 40
What is the value of (x - y)^4?  [#permalink]

### Show Tags

27 Feb 2012, 09:17
3
00:00

Difficulty:

25% (medium)

Question Stats:

67% (00:44) correct 33% (00:46) wrong based on 188 sessions

### HideShow timer Statistics

What is the value of (x - y)^4?

(1) The product of x and y is 7.
(2) x and y are integers.
Math Expert
Joined: 02 Sep 2009
Posts: 49251
Re: What is the value  [#permalink]

### Show Tags

27 Feb 2012, 09:20
2
4
What is the value of (x - y)^4?

(1) The product of x and y is 7, well this one is clearly insufficient: if $$x=7$$ and $$y=1$$ then $$(x-y)^4=6^4$$ and if $$x=14$$ and $$y=\frac{1}{2}$$ then $$(x-y)^4=(\frac{27}{2})^4$$, two different answers, hence not sufficient.

(2) x and y are integers. Also insufficient.

(1)+(2) As $$x$$ and $$y$$ are integers and $$xy=7$$ then either $$x$$ and $$y$$ are 1 and 7 (or vise-versa) or -1 and -7 (or vise-versa) in any case because of even power: $$(x-y)^4=(7-1)^4=(1-7)^4=(-7+1)^4=(-1+7)^4=6^4$$. Sufficient.

_________________
##### General Discussion
Intern
Joined: 03 Aug 2014
Posts: 16
Re: What is the value of (x - y)^4?  [#permalink]

### Show Tags

16 Jan 2015, 21:03
why can't x = -1 and y = -7 or vice versa?
EMPOWERgmat Instructor
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 12415
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Re: What is the value of (x - y)^4?  [#permalink]

### Show Tags

17 Jan 2015, 12:21
Hi cg0588,

You ask a good question. X and Y CAN be -1 and -7 (or vice versa). Thankfully, it's easy to prove what happens when either of those options occurs:

(X - Y)^4

First, the positive options:
X = 1, Y = 7
(1 - 7)^4 = (-6)^4 = 1296

X = 7, Y = 1
(7 - 1)^4 = (6)^4 = 1296

Now, the negative options:
X = -1, Y = -7
(-1 -[-7]) = (6)^4 = 1296

X = -7, Y = -1
(-7 - [-1]) = (-6)^4 = 1296

The result stays the SAME.

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

Co-Founder & 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!***********************

Non-Human User
Joined: 09 Sep 2013
Posts: 8095
Re: What is the value of (x - y)^4?  [#permalink]

### Show Tags

24 Apr 2017, 06:56
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.
_________________
Re: What is the value of (x - y)^4? &nbs [#permalink] 24 Apr 2017, 06:56
Display posts from previous: Sort by

# Events & Promotions

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.