It is currently 23 Nov 2017, 12:08

### 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

# m13 #13 The unlucky 13!

Author Message
Senior Manager
Joined: 18 Aug 2009
Posts: 299

Kudos [?]: 364 [0], given: 9

m13 #13 The unlucky 13! [#permalink]

### Show Tags

16 Nov 2009, 22:19
Is $$(x - y)*(x + y)$$ an even integer?

1. $$x$$ and $$y$$ are integers
2. $$x + y$$ is even

Chose incorrect B and after looking at the solution thought of adding a little to OE (don't know if it is a superstition, but I'm getting #13 wrong in so many tests )...

x+y is even

in case both are integers, then they are either both odd or both even => x-y will be even.

in case both are fraction (if only 1 is fraction, then "x+y is even" does not holds true). Check it with few substitutions for odd/even combination on denominator so as to keep x+y even:
Even denominator... 1/2+3/2 => subtraction result odd. But overall result even.
Odd denominator... 5/3+1/3 => subtraction result is fraction making B false
So they have to be integers OA
[Reveal] Spoiler:
C

Kudos [?]: 364 [0], given: 9

Senior Manager
Joined: 18 Aug 2009
Posts: 299

Kudos [?]: 364 [0], given: 9

Re: m13 #13 The unlucky 13! [#permalink]

### Show Tags

16 Nov 2009, 22:23
'am I glad that it not my 13th post on Friday the 13th

Kudos [?]: 364 [0], given: 9

Intern
Joined: 09 Nov 2009
Posts: 2

Kudos [?]: [0], given: 0

Re: m13 #13 The unlucky 13! [#permalink]

### Show Tags

22 Nov 2009, 08:48
S1 is insufficient
s2 is sufficient because
(x-y) is either even or odd integer, but multiplication with even (x+y) will always be even. So it is sufficient to tell us the given statement result.

Kudos [?]: [0], given: 0

Senior Manager
Affiliations: PMP
Joined: 13 Oct 2009
Posts: 296

Kudos [?]: 175 [0], given: 37

Re: m13 #13 The unlucky 13! [#permalink]

### Show Tags

22 Nov 2009, 09:42
gbansal745 wrote:
S1 is insufficient
s2 is sufficient because
(x-y) is either even or odd integer, but multiplication with even (x+y) will always be even. So it is sufficient to tell us the given statement result.

Ans. shud be C as we need to know that x,y are integers.

Consider x=13/4, y = 11/4, then x+y=6 and x-y=1/2 and (x-y) (x+y) = 3 (odd)
_________________

Thanks, Sri
-------------------------------
keep uppp...ing the tempo...

Press +1 Kudos, if you think my post gave u a tiny tip

Kudos [?]: 175 [0], given: 37

Re: m13 #13 The unlucky 13!   [#permalink] 22 Nov 2009, 09:42
Display posts from previous: Sort by

# m13 #13 The unlucky 13!

Moderator: 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®.