Is x^2*y^4 divisible by 49? (1) x is an integer : DS Archive
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# Is x^2*y^4 divisible by 49? (1) x is an integer

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Director
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Is x^2*y^4 divisible by 49? (1) x is an integer [#permalink]

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10 Jul 2005, 08:24
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27) Is x^2*y^4 divisible by 49?
(1) x is an integer divisible by 7
(2) x*y is an integer divisible by 49.
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10 Jul 2005, 09:11
hmm

I would go with D, but then think about it, we dont know if Y is an integer or not! I would say B it is...

from ...
1)

X=7K, then X^2=49.K^2

we dont know what Y is? say Y^4=1/49...

then in that case X^2.Y^4= [(49.K^2)(1/49)]49....

that means K^2/49 has to be an integer, but we dont know what K is ?....

therefore Insuff

2)

X.Y=k.49

x^2.y^4= [(x^2.Y^2)(y^2)]=> [(k.49)^2.Y^2]/49, as we can see 49 cancels...sufficient....

B it is....
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10 Jul 2005, 11:47
I will go with D
fresinha12, The question is asking only if there are 2 7s in x^2*y^4 and not about integers.
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10 Jul 2005, 14:00
I am thinking the question is aksing is X^2Y^4 a multiple of 49?

without knowing what Y is we cant really know right?

the question is aksing X^2Y^4=K.49?

statement 1) says x=7K, therefore x^2=49K right!

[(49K)*(y^4)]/49, without knowing what Y is we dont know...

2) same problem...

sorry I meant the answer should be E...I dont know how I said B...it is clearly E!

I will go with D
fresinha12, The question is asking only if there are 2 7s in x^2*y^4 and not about integers.
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10 Jul 2005, 14:51
So is it the 'y' which is forcing the answer to be E?
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13 Jul 2005, 03:43
thanks fresinha. also made the same error in my previous choice of (D).
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14 Jul 2005, 04:18
the question is asking if "Is x^2*y^4 divisible by 49?" from A) we can say that it is divisible by 49 so A) is corect, same for B) we can factor out X*Y and say that it is divisible by 49.
D seems correct to me or i don't get the logic behind E)
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14 Jul 2005, 07:57
E)...

consider: x=49^2 and y=1/49 or x=7 and y=7
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22 Jul 2005, 15:03
hello
can anyone explains me why B is not sufficient
thanks
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22 Jul 2005, 17:42
mandy wrote:
hello
can anyone explains me why B is not sufficient
thanks

Mandy,
I think B is wrong if you assume x is 98 (an integer) and y is 1/2(not an integer)

98 * 1/2 = 49 and 49 is divisible by 49.

Howerver if you the values of X and Y in statement 2 into the stem,

98^2 * 1/2^4
= 9604 * 1/16
the answerr is not an integer thus it stmt 2 is not sufficient to conclude the stem is divisible by 49.
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24 Jul 2005, 04:53
Folaa3 wrote:
mandy wrote:
hello
can anyone explains me why B is not sufficient
thanks

Mandy,
I think B is wrong if you assume x is 98 (an integer) and y is 1/2(not an integer)

98 * 1/2 = 49 and 49 is divisible by 49.

Howerver if you the values of X and Y in statement 2 into the stem,

98^2 * 1/2^4
= 9604 * 1/16
the answerr is not an integer thus it stmt 2 is not sufficient to conclude the stem is divisible by 49.

thanks Folaa
24 Jul 2005, 04:53
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