It is currently 21 Sep 2017, 05:29

Close

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
Your Progress

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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If x and y are positive integers, is xy a multiple of 8? (1)

  post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
SVP
SVP
avatar
Joined: 21 Jul 2006
Posts: 1513

Kudos [?]: 978 [0], given: 1

If x and y are positive integers, is xy a multiple of 8? (1) [#permalink]

Show Tags

New post 11 Dec 2007, 03:47
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

50% (00:00) correct 50% (01:31) wrong based on 1 sessions

HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

If x and y are positive integers, is xy a multiple of 8?

(1) The greatest common divisor of x and y is 10

(2) The least common myltiple of x and y is 100


Please explain your answer

Kudos [?]: 978 [0], given: 1

Director
Director
avatar
Joined: 09 Aug 2006
Posts: 754

Kudos [?]: 239 [0], given: 0

Re: DS: GCM & LCM [#permalink]

Show Tags

New post 11 Dec 2007, 03:59
tarek99 wrote:
If x and y are positive integers, is xy a multiple of 8?

(1) The greatest common divisor of x and y is 10

(2) The least common myltiple of x and y is 100


Please explain your answer


I think the answer is B.

Stat 1:
If x = 10 y = 10 then xy is not a multiple of 8
If x = 20 y = 30 then xy is a multiple of 8
Insuff.

Stat 2:
If LCM is 100 then the integers can be expressed as 100x and 100y. 100x * 100y is always divisible by 8. Sufficient.

Kudos [?]: 239 [0], given: 0

Intern
Intern
avatar
Joined: 25 Nov 2007
Posts: 38

Kudos [?]: 12 [0], given: 0

Re: DS: GCM & LCM [#permalink]

Show Tags

New post 11 Dec 2007, 10:35
GK_Gmat wrote:
tarek99 wrote:
If x and y are positive integers, is xy a multiple of 8?

(1) The greatest common divisor of x and y is 10

(2) The least common myltiple of x and y is 100


Please explain your answer


I think the answer is B.

Stat 1:
If x = 10 y = 10 then xy is not a multiple of 8
If x = 20 y = 30 then xy is a multiple of 8
Insuff.

Stat 2:
If LCM is 100 then the integers can be expressed as 100x and 100y. 100x * 100y is always divisible by 8. Sufficient.


Answer A

(1) The greatest common divisor of x and y is 10

Meaning 10*a =x and 10*b=y . Meaning that xy = 100 ab , Neither a nor b can be even, because that will increase the GCD above 10. and multiplication of two odd numbers ab cannot be divisble by 8, 100ab is not divisible by 8 either ... Sufficient.


(2) The least common myltiple of x and y is 100 .
if x=5 and y =100 , XY is not mulitple of 8
if x=20 and y =100 XY is multiple of 8

Whats the OA

Kudos [?]: 12 [0], given: 0

Manager
Manager
avatar
Joined: 29 Jul 2007
Posts: 182

Kudos [?]: 36 [0], given: 0

 [#permalink]

Show Tags

New post 11 Dec 2007, 18:23
C.

If x, y >0; does XY/8 = int?

only if XY has 3 2's as 8 = 2^3

I. GCF is 10 or 2*5. GCF takes only factors that are common to both numbers. So all we know is that there are 2 2's for sure. There may be more, but we don't know.

II. LCD is 100 or 5^2*2^2. LCD takes the higher power of each factor. So all we know is that one of the two numbers has 2 2's in it. We are not sure if there is a 3rd 2 in the mix or not.

I and II taken together is sufficient. By I, we know that both numbers have a 2 in their factorization. By II, we know that one of the numbers (or both) have 2 2's (or 2^2) in their factorization. So taken together, we know for sure that there are at least 3 2's when X*Y.

Kudos [?]: 36 [0], given: 0

Director
Director
User avatar
Joined: 03 Sep 2006
Posts: 869

Kudos [?]: 1030 [0], given: 33

GMAT ToolKit User
Re: DS: GCM & LCM [#permalink]

Show Tags

New post 11 Dec 2007, 18:48
tarek99 wrote:
If x and y are positive integers, is xy a multiple of 8?

(1) The greatest common divisor of x and y is 10

(2) The least common myltiple of x and y is 100


Please explain your answer


Answer should be "C".

From(i); GCD is 10, numbers can be any combination of multiples of 10, for example; 10&20, 10&30. One of the is multiple of 8 and other isn't.

From (ii); LCM is 100, again it can be any combination of numbers such as ;
5&100, 20&100. One of the is multiple of 8 and other isn't.

LCM*GCF=product of numbers


Check this link

http://www.gmatclub.com/forum/t56958

Kudos [?]: 1030 [0], given: 33

Retired Moderator
User avatar
Joined: 18 Jul 2008
Posts: 964

Kudos [?]: 285 [0], given: 5

Re: DS: GCM & LCM [#permalink]

Show Tags

New post 19 Jan 2009, 15:31
LCM*GCF=product of numbers[/size]

Can someone explain the above?

LM wrote:
tarek99 wrote:
If x and y are positive integers, is xy a multiple of 8?

(1) The greatest common divisor of x and y is 10

(2) The least common myltiple of x and y is 100


Please explain your answer


Answer should be "C".

From(i); GCD is 10, numbers can be any combination of multiples of 10, for example; 10&20, 10&30. One of the is multiple of 8 and other isn't.

From (ii); LCM is 100, again it can be any combination of numbers such as ;
5&100, 20&100. One of the is multiple of 8 and other isn't.

LCM*GCF=product of numbers


Check this link

http://www.gmatclub.com/forum/t56958

Kudos [?]: 285 [0], given: 5

Director
Director
avatar
Joined: 29 Aug 2005
Posts: 855

Kudos [?]: 472 [0], given: 7

Re: DS: GCM & LCM [#permalink]

Show Tags

New post 19 Jan 2009, 15:46
The simplest way is to test with actual numbers :-D
LCM of 8 and 10 is 40
GCD is 2
8*10=2*40

Kudos [?]: 472 [0], given: 7

Manager
Manager
User avatar
Joined: 25 Aug 2007
Posts: 115

Kudos [?]: 15 [0], given: 0

Location: NYC Baby!!!
Re: DS: GCM & LCM [#permalink]

Show Tags

New post 19 Jan 2009, 16:32
Wow it is C

yes LCF*GCD= product which you can then divide by 8

10*100= 1000/8 = 125

Kudos [?]: 15 [0], given: 0

Intern
Intern
avatar
Joined: 19 Jan 2009
Posts: 17

Kudos [?]: 4 [0], given: 0

Re: DS: GCM & LCM [#permalink]

Show Tags

New post 19 Jan 2009, 23:29
stmnt 1 : in sufficient
stmnt 2 : insufficient

combined :

lcm . gcd = x.y

1000 = xy

and 1000 is multiple of 8 .

so answer is C.

www.graduatetutor.com

Kudos [?]: 4 [0], given: 0

Re: DS: GCM & LCM   [#permalink] 19 Jan 2009, 23:29
Display posts from previous: Sort by

If x and y are positive integers, is xy a multiple of 8? (1)

  post reply Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

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®.