GMAT Changed on April 16th - Read about the latest changes here

 It is currently 24 Apr 2018, 00:05

### 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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# M15-23

Author Message
TAGS:

### Hide Tags

Senior Manager
Joined: 08 Jun 2015
Posts: 476
Location: India
GMAT 1: 640 Q48 V29

### Show Tags

27 Jan 2017, 07:54
Good catch ... thanks for posting this question.
_________________

" The few , the fearless "

Intern
Joined: 11 Aug 2017
Posts: 2
Location: India

### Show Tags

15 Dec 2017, 09:41
Bunuel wrote:
Official Solution:

(1) $$x$$ and $$y$$ are even integers. Clearly insufficient, consider $$x=y=0$$ for an YES answer and $$x=2$$ and $$y=0$$ for a NO answer.

(2) $$x + y$$ is divisible by $$8$$. Now, $$x^2 - y^2=(x+y)(x-y)$$, if one of the multiples is divisible by 8 then so is the product: true for integers, but we are not told that $$x$$ and $$y$$ are integers. If $$x=4.8$$ and $$y=3.2$$, $$x+y$$ is divisible by $$8$$, BUT $$x^2 - y^2$$ is not. Not sufficient.

(1)+(2) $$x$$ and $$y$$ integers. $$x+y$$ divisible by 8. Hence $$(x+y)(x-y)$$ is divisible by $$8$$. Sufficient.

What if X-Y is Negative? We know they're even integers but don't know if X>Y or not.
Math Expert
Joined: 02 Sep 2009
Posts: 44652

### Show Tags

15 Dec 2017, 09:43
sambha wrote:
Bunuel wrote:
Official Solution:

(1) $$x$$ and $$y$$ are even integers. Clearly insufficient, consider $$x=y=0$$ for an YES answer and $$x=2$$ and $$y=0$$ for a NO answer.

(2) $$x + y$$ is divisible by $$8$$. Now, $$x^2 - y^2=(x+y)(x-y)$$, if one of the multiples is divisible by 8 then so is the product: true for integers, but we are not told that $$x$$ and $$y$$ are integers. If $$x=4.8$$ and $$y=3.2$$, $$x+y$$ is divisible by $$8$$, BUT $$x^2 - y^2$$ is not. Not sufficient.

(1)+(2) $$x$$ and $$y$$ integers. $$x+y$$ divisible by 8. Hence $$(x+y)(x-y)$$ is divisible by $$8$$. Sufficient.

What if X-Y is Negative? We know they're even integers but don't know if X>Y or not.

Can't a negative integer be divisible by 8? For example, -8 IS divisible by 8.
_________________
Re: M15-23   [#permalink] 15 Dec 2017, 09:43

Go to page   Previous    1   2   [ 23 posts ]

Display posts from previous: Sort by

# M15-23

Moderators: chetan2u, Bunuel

 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®.