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a, b, c, and d are integers; abcd≠0

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a, b, c, and d are integers; abcd≠0 [#permalink] New post 15 Jan 2012, 23:43
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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 here
[Reveal] Spoiler:
http://www.platinumgmat.com/gmat-practice-test/?state=qc-cn#show-explanation


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?
[Reveal] Spoiler: OA
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Re: a, b, c, and d are integers; abcd≠0 [#permalink] New post 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.
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Re: a, b, c, and d are integers; abcd≠0 [#permalink] New post 16 Jan 2012, 02:11
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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. 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.
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Re: a, b, c, and d are integers; abcd≠0 [#permalink] New post 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.
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Re: a, b, c, and d are integers; abcd≠0 [#permalink] New post 16 Jan 2012, 03:19
thanks for explanation, you should agree very stupid and easy question, I should sleep more not to make such mistakes....
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Re: a, b, c, and d are integers; abcd≠0 [#permalink] New post 21 Jan 2012, 13:45
a, b, c, and d are integers; abcd >< 0; what is the value of cd?

1) c/b = 2/d

c = (2*b)/(d)
not sufficient

2) b^3*a^4*c = 27*a^4*c

b^3 = 27
b = 3

not sufficient.

1 + 2

c = (2*3)/d
c = (6)/d
cd = 6

sufficient.

sufficient.
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Re: a, b, c, and d are integers; abcd≠0 [#permalink] New post 17 May 2012, 08:22
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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.
.



Bunuel, i think what you meant here is Not Sufficient. Correct?
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Re: a, b, c, and d are integers; abcd≠0 [#permalink] New post 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] New post 13 Sep 2012, 07:18
Expert's post
fameatop wrote:
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.


Thank you. Typo edited.
_________________

NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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Re: a, b, c, and d are integers; abcd≠0   [#permalink] 13 Sep 2012, 07:18
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