Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 12 Feb 2016, 06:12

### 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

# Is x^2 - y^2 divisible by 8? 1. x and y are even integers 2.

Author Message
Manager
Joined: 22 May 2007
Posts: 217
Followers: 2

Kudos [?]: 53 [0], given: 0

Is x^2 - y^2 divisible by 8? 1. x and y are even integers 2. [#permalink]  28 Jul 2008, 19:39
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Is $$x^2 - y^2$$ divisible by 8?

1. x and y are even integers
2. x + y is divisible by 8
Director
Joined: 27 May 2008
Posts: 549
Followers: 8

Kudos [?]: 257 [0], given: 0

Re: x2 [#permalink]  28 Jul 2008, 19:43
aaron22197 wrote:
Is $$x^2 - y^2$$ divisible by 8?

1. x and y are even integers
2. x + y is divisible by 8

statement 1 : not suff

statement 2 : looks suff but wait... what if x = 5.25 and y = 2.75, (x+y) = 8 and (x-y) = 2.5
so x^2 - y^2 is not divisible by 8, even though x+y is..... not suff

combine both ... suff Option C
Manager
Joined: 03 Jun 2008
Posts: 136
Schools: ISB, Tuck, Michigan (Ross), Darden, MBS
Followers: 2

Kudos [?]: 20 [0], given: 0

Re: x2 [#permalink]  28 Jul 2008, 19:45
Statement 1 not sufficient

Statement 2: Divisible by 8 since (x+y)(x-y)
_________________

-----------------------------------------------------------
'It's not the ride, it's the rider'

SVP
Joined: 07 Nov 2007
Posts: 1820
Location: New York
Followers: 29

Kudos [?]: 647 [0], given: 5

Re: x2 [#permalink]  29 Jul 2008, 11:21
GMBA85 wrote:
Statement 1 not sufficient

Statement 2: Divisible by 8 since (x+y)(x-y)

Agree with durgesh unless question says x,y are integers...

(5.25+2.75) (5.25-2.75) = 8* 2.50 = not divisible.
_________________

Smiling wins more friends than frowning

Current Student
Joined: 28 Dec 2004
Posts: 3385
Location: New York City
Schools: Wharton'11 HBS'12
Followers: 14

Kudos [?]: 208 [0], given: 2

Re: x2 [#permalink]  29 Jul 2008, 13:54
aaron22197 wrote:
Is $$x^2 - y^2$$ divisible by 8?

1. x and y are even integers
2. x + y is divisible by 8

I get B..

x^2 - y^2 = (x+y)(x-y) regardless if x or y are integers..

(x-y)(x+y) where (x+y)=8*M then i think x^2 - y^2 is divisble by 8..
Current Student
Joined: 28 Dec 2004
Posts: 3385
Location: New York City
Schools: Wharton'11 HBS'12
Followers: 14

Kudos [?]: 208 [0], given: 2

Re: x2 [#permalink]  29 Jul 2008, 17:25
durgesh79 wrote:
aaron22197 wrote:
Is $$x^2 - y^2$$ divisible by 8?

1. x and y are even integers
2. x + y is divisible by 8

statement 1 : not suff

statement 2 : looks suff but wait... what if x = 5.25 and y = 2.75, (x+y) = 8 and (x-y) = 2.5
so x^2 - y^2 is not divisible by 8, even though x+y is..... not suff

combine both ... suff Option C

wow..totally agree..great work...
VP
Joined: 17 Jun 2008
Posts: 1397
Followers: 8

Kudos [?]: 205 [0], given: 0

Re: x2 [#permalink]  03 Aug 2008, 10:17
aaron22197 wrote:
Is $$x^2 - y^2$$ divisible by 8?

1. x and y are even integers
2. x + y is divisible by 8

Clearly (1) is not sufficient since when x=4,y=2 the logic fails
(2)since x^2-y^2=x-y * x+y hence (2) is SUFFI

IMO B
_________________

cheers
Its Now Or Never

Manager
Joined: 22 May 2007
Posts: 217
Followers: 2

Kudos [?]: 53 [0], given: 0

Re: x2 [#permalink]  04 Aug 2008, 04:55
OA is C. Good discussion
Retired Moderator
Joined: 18 Jul 2008
Posts: 994
Followers: 10

Kudos [?]: 136 [0], given: 5

Re: x2 [#permalink]  04 Aug 2008, 06:22
Yes, I came to the same conclusion, algebraically. But it seems wrong when plugged in numbers as above.

But why is our approach wrong?

spriya wrote:
aaron22197 wrote:
Is $$x^2 - y^2$$ divisible by 8?

1. x and y are even integers
2. x + y is divisible by 8

Clearly (1) is not sufficient since when x=4,y=2 the logic fails
(2)since x^2-y^2=x-y * x+y hence (2) is SUFFI

IMO B
VP
Joined: 17 Jun 2008
Posts: 1397
Followers: 8

Kudos [?]: 205 [0], given: 0

Re: x2 [#permalink]  04 Aug 2008, 09:18
Yes, I came to the same conclusion, algebraically. But it seems wrong when plugged in numbers as above.

But why is our approach wrong?

spriya wrote:
aaron22197 wrote:
Is $$x^2 - y^2$$ divisible by 8?

1. x and y are even integers
2. x + y is divisible by 8

Clearly (1) is not sufficient since when x=4,y=2 the logic fails
(2)since x^2-y^2=x-y * x+y hence (2) is SUFFI

IMO B

Thats because we want integers for divisibility and we dont have one
_________________

cheers
Its Now Or Never

Senior Manager
Joined: 06 Apr 2008
Posts: 449
Followers: 1

Kudos [?]: 90 [0], given: 1

Re: x2 [#permalink]  05 Aug 2008, 02:01
aaron22197 wrote:
Is $$x^2 - y^2$$ divisible by 8?

1. x and y are even integers
2. x + y is divisible by 8

$$x^2 - y^2$$ = (x +y)(x - y)

So if x + y is divisible by 8 then $$x^2 - y^2$$ should be divisible as well but only when x,y are integers.

Therefore C)
Retired Moderator
Joined: 18 Jul 2008
Posts: 994
Followers: 10

Kudos [?]: 136 [0], given: 5

Re: x2 [#permalink]  05 Aug 2008, 15:32
Thanks. That makes sense now. I never knew that to be true. Always thought X,Y could be all numbers.
Re: x2   [#permalink] 05 Aug 2008, 15:32
Display posts from previous: Sort by