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16 Jan 2012, 00:43
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Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
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a, b, c, and d are integers; abcd ≠ 0; what is the value of cd?
(1) \(\frac{c}{b} = \frac{2}{d}\)
(2) \(b^3*a^4*c = 27*a^4*c\)
(1) \(\frac{c}{b} = \frac{2}{d}\)
(2) \(b^3*a^4*c = 27*a^4*c\)
solution here https://www.platinumgmat.com/gmat-practi ... xplanation
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?
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?
Updated on: 16 Jan 2012, 03:30
Originally posted by 321kumarsushant on 16 Jan 2012, 02:09.
Last edited by 321kumarsushant on 16 Jan 2012, 03:30, edited 2 times in total.
Last edited by 321kumarsushant on 16 Jan 2012, 03:30, edited 2 times in total.
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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
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
16 Jan 2012, 03:11
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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:
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.
(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
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.
