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# gmat prep multiple

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Manager
Joined: 28 Aug 2006
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gmat prep multiple [#permalink]  01 Jan 2007, 20:18
Could some one explain this
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Manager
Joined: 19 Aug 2006
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A it is.

Stmt 1) 3y^2 + 7y =x
y( 3y +7 ) = x, if x and y are integers then clearly sufficient.

Stmt 2) (x^2 - x)/y is integer
x(x-1) /y = int so x or x-1 may be multiple of y or both
may be multiple of y not sure. So not sufficient.
Senior Manager
Joined: 24 Nov 2006
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(1) 3*y^2 + 7*y = multiple of y. Suff.

(2) x^2 - x. Let x=3: x^2 - x = 6 is multiple of y, but x=3 is not necessarily multiple of y. Let x=2: x^2 - x = 2 is multiple of y, then x=2 is also multiple of y. Insuff.

A.
Manager
Joined: 26 Aug 2006
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Information given in the stem: x and y are integers and greater than 1
Question : Is x multiple of y i.e. x=k(y) where k is a multiple means an integer
Statement 1: 3y2+7y=x
(3y+7)=x/y since we know y> 1 and integers, for all values of y, say 2,3, etc. 3y+7 will yield an integer. This is sufficient

Statement 2: x2-x=k(y)( K is a multiple, it means it is an integer)
x(x-1)=k(y)
(x-1)/k =y/x, now we know that x>1 and k is an integer, so for x=2 and k=2 or 3 etc. y/x is not necessarily an integer. Hence not sufficient.

VP
Joined: 28 Mar 2006
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Guys I didnt understand why A is the correct answer

we have 3*y^2 + 7*y =x

we are asked if x is a amultiple of y

which means y/x =k where k is a integer

y(3y + 7) = x

y/x = 1/(3y+7)

So if y/x is a fraction how is that it is a multiple of y?

Thanks!
Manager
Joined: 28 Aug 2006
Posts: 245
Location: Albuquerque, NM
Followers: 1

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

y/x can be a fraction if x is a multiple of y
VP
Joined: 28 Mar 2006
Posts: 1384
Followers: 2

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

Yep got it....wasnt concentrating much I think...

Thanks guys!
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