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brief expl from me 1 - clearly not suff, and we got that cd=2b 2 - clearly not suff, and we got that |b^3|=27 cause what if c negative? so we can't say for sure that b=3 like stated in OA. Am I right?

Re: a, b, c, and d are integers; abcd≠0 [#permalink]

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16 Jan 2012, 01:09

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a, b, c, and d are integers; abcd >< 0; what is the value of cd? 1) c/b = 2/d 2) b^3*a^4*c = 27*a^4*c

SOLUTION:

statement 1: c/b = 2/d cd = 2b, we don't know the value of b. so. we can't find the value of cd. NOT SUFFICIENT

statement 2 : b^3*a^4*c = 27*a^4*c ==> a^4 * c (b^3-27) = 0 it means, a^4 =0 or c =0 or b^3 =27 so, b = 3 so, here we can get different values of cd. NOT SUFFICIENT

after combining both statement , we can get value of cd = 2b =6

Hence the ans is C.

I HOPE IT WILL BE HELPFUL. PS: EDITED after bunuel explanation
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Last edited by 321kumarsushant on 16 Jan 2012, 02:30, edited 2 times in total.

a, b, c, and d are integers; abcd≠0; what is the value of cd?

(1) c/b = 2/d --> \(cd=2b\), we don't know the value of \(b\) to get the single numerical value of \(cd\). Not sufficient.

(2) b^3*a^4*c = 27*a^4*c --> as \(a\) and \(c\) does not equal to zero we can safely reduce both parts by \(a^4*c\) --> \(b^3=27\) --> \(b=3\). Not sufficient.

(1)+(2) As from (1) \(cd=2b\) and from (2) \(b=3\) then \(cd=2b=6\). Sufficient.

Answer:C.

As for your question:

Runner2 wrote:

2 - clearly not suff, and we got that |b^3|=27 cause what if c negative? so we can't say for sure that b=3 like stated in OA. Am I right?

Odd roots have the same sign as the base of the root. For example, \(\sqrt[3]{125} =5\) and \(\sqrt[3]{-64} =-4\).

So \(\sqrt[3]{27}=3\) and not \(-3\) --> \(3^3=27\) and \((-3)^3=-27\).

Re: a, b, c, and d are integers; abcd≠0 [#permalink]

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13 Sep 2012, 07:12

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Bunuel wrote:

a, b, c, and d are integers; abcd≠0; what is the value of cd?

(1) c/b = 2/d --> \(cd=2b\), we don't know the value of \(b\) to get the single numerical value of \(cd\). Sufficient.

(2) b^3*a^4*c = 27*a^4*c --> as \(a\) and \(c\) does not equal to zero we can safely reduce both parts by \(a^4*c\) --> \(b^3=27\) --> \(b=3\). Not sufficient.

(1)+(2) As from (1) \(cd=2b\) and from (2) \(b=3\) then \(cd=2b=6\). Not sufficient.

Answer:C.

As for your question:

Runner2 wrote:

2 - clearly not suff, and we got that |b^3|=27 cause what if c negative? so we can't say for sure that b=3 like stated in OA. Am I right?

Odd roots have the same sign as the base of the root. For example, \(\sqrt[3]{125} =5\) and \(\sqrt[3]{-64} =-4\).

So \(\sqrt[3]{27}=3\) and not \(-3\) --> \(3^3=27\) and \((-3)^3=-27\).

Hope its' clear.

Hi Bunuel,

There is a slight typing error in the explanation. Statement "(1) c/b = 2/d --> \(cd=2b\), we don't know the value of \(b\) to get the single numerical value of \(cd\). Sufficient." should read "(1) c/b = 2/d --> \(cd=2b\), we don't know the value of \(b\) to get the single numerical value of \(cd\). Insufficient."

Correct me if i am wrong.
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Re: a, b, c, and d are integers; abcd≠0 [#permalink]

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16 Jan 2012, 02:33

@bunuel thanks for explanation. it looks that my mind was somewhere else while solving the question. many times i misses an obvious point , main reason never to the 51 in Quant. i will have to focus more.

anyway, i have edited my explanation.
_________________

kudos me if you like my post.

Attitude determine everything. all the best and God bless you.

a, b, c, and d are integers; abcd≠0; what is the value of cd?

(1) c/b = 2/d --> \(cd=2b\), we don't know the value of \(b\) to get the single numerical value of \(cd\). Sufficient.

(2) b^3*a^4*c = 27*a^4*c --> as \(a\) and \(c\) does not equal to zero we can safely reduce both parts by \(a^4*c\) --> \(b^3=27\) --> \(b=3\). Not sufficient.

(1)+(2) As from (1) \(cd=2b\) and from (2) \(b=3\) then \(cd=2b=6\). Not sufficient.

Answer:C.

As for your question:

Runner2 wrote:

2 - clearly not suff, and we got that |b^3|=27 cause what if c negative? so we can't say for sure that b=3 like stated in OA. Am I right?

Odd roots have the same sign as the base of the root. For example, \(\sqrt[3]{125} =5\) and \(\sqrt[3]{-64} =-4\).

So \(\sqrt[3]{27}=3\) and not \(-3\) --> \(3^3=27\) and \((-3)^3=-27\).

Hope its' clear.

Hi Bunuel,

There is a slight typing error in the explanation. Statement "(1) c/b = 2/d --> \(cd=2b\), we don't know the value of \(b\) to get the single numerical value of \(cd\). Sufficient." should read "(1) c/b = 2/d --> \(cd=2b\), we don't know the value of \(b\) to get the single numerical value of \(cd\). Insufficient."

Re: a, b, c, and d are integers; abcd≠0 [#permalink]

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02 Feb 2016, 03:49

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