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hpgmat: Senior | Next Rank: 100 Posts; Posts: 75; Joined: Thu Aug 20, 2009 11:55 am; Location: vancouver, B.C; GMAT Score:640

by hpgmat » Tue Dec 08, 2009 8:01 pm

if x and y are integers greather than 1 , is x a multiple of y?

1) 3(y^2) + 7y = x

2) x^2- x is multiple of y

my approach :

x multiple of y translates to : is X = A Y ??

1) Y (3Y+7) = X ....> now x is written as AY ( with (3Y + 7) being A)

2) x^2 - x = B Y ....> x (x-1) = B Y ...> X = (B/(x-1)) Y ....> X is written as AY ( with B/(x-1) being A

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Source: Beat The GMAT — Data Sufficiency | Tue Dec 08, 2009 8:01 pm

bou_k: Newbie | Next Rank: 10 Posts; Posts: 4; Joined: Mon Dec 07, 2009 11:23 pm

by bou_k » Wed Dec 09, 2009 1:58 am

you have a problem B/(x-1)) is not an integer in general so the ans is only A)

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adamsmith2009: Senior | Next Rank: 100 Posts; Posts: 36; Joined: Fri Mar 27, 2009 6:53 pm

by adamsmith2009 » Wed Dec 09, 2009 8:33 am

A) Not sufficient. X could be 3 which would make Y= 34 or X could be 2 which would make Y= 20.

B) Sufficient. x(x-1) = multiple of Y

So if x is 3 y is a multiple of 6. Therefore the minimum number y could be would be 6. So x can't be a multiple of y.
If x is 5 y is a multiple of 20. Therefore the minimum number y could be would be 20. So x can't be a multiple of y. X is always less than Y.

What's the OA?

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November Rain: Senior | Next Rank: 100 Posts; Posts: 50; Joined: Tue Oct 13, 2009 1:25 am; Thanked: 14 times; GMAT Score:720

by November Rain » Wed Dec 09, 2009 10:16 am

Hi
I think it's E. Could you please let us know the OA?

A is insufficient - If you add two numbers multiple of Y and theresult is a multiple of X doesn't mean that Y is a multiple of X on its own.

B is also insufficient - It can be rephrased into x(x-1) is a multiple of Y. However, the number that can allow Y to become multiple of x(x-1) might be X-1 or X. So, also insufficient.

Both statements together don't seem to add any new information to each other. So, its E.

Could anyone confirm the OA?

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hpgmat: Senior | Next Rank: 100 Posts; Posts: 75; Joined: Thu Aug 20, 2009 11:55 am; Location: vancouver, B.C; GMAT Score:640

by hpgmat » Wed Dec 09, 2009 11:55 am

adamsmith2009 wrote:A) Not sufficient. X could be 3 which would make Y= 34 or X could be 2 which would make Y= 20.

B) Sufficient. x(x-1) = multiple of Y

So if x is 3 y is a multiple of 6. Therefore the minimum number y could be would be 6. So x can't be a multiple of y.
If x is 5 y is a multiple of 20. Therefore the minimum number y could be would be 20. So x can't be a multiple of y. X is always less than Y.

What's the OA?

you are thinking x factor of y . question is saying x multiple of y

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