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If ab/cd < 0 , is bc > ad (1) cd > ab (2) b < c < 0

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If ab/cd < 0 , is bc > ad (1) cd > ab (2) b < c < 0 [#permalink] New post 15 Aug 2009, 23:46
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If ab/cd < 0 , is bc > ad

(1) cd > ab

(2) b < c < 0
[Reveal] Spoiler: OA

Last edited by Bunuel on 30 Jan 2012, 15:00, edited 1 time in total.
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Re: is bc>ad? [#permalink] New post 16 Aug 2009, 07:56
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IMO B
given ab/cd < 0 , so two cases
1) ab < 0, cd >0 or
2) ab >0 , cd <0

stmt 1 cd > ab
so case 1 satisfy, qstn is bc > ad? not sufficnt

stmt 2
b<c<0
applying in above two cases

1) ab<0 , cd> 0
b< 0 , so for ab<0, a must be >0
c<0 , so for cd>0, d must be <0

so a>0, b<0, c<0, d<0 , apply to check bc > ad?
defintely bc>ad

2) ab >0 , cd < 0

b<0 , so for ab>0 , a must be <0
c<0 , so for cd<0 , d must be >0

so a<0, b<0, c<0, d>0 , apply to check bc>ad?
defintely bc>ad.
so stmt2 suffint
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Re: is bc>ad? [#permalink] New post 16 Aug 2009, 07:56
given

ab/cd<0


case 1 a,b are positive and either c or d is negative

case 2 c,d are positive and either a or b is negative

case 3 a,b are negative and either c or d negative

case 4 c,d are negative and either a or b negative



st1 - cd>ab

we have to consider case 2 and case 4

i.e c,d both are postive or negative and either a or b postive

case 2:
consider cd postive and a negative,b positive

so will get bc>ad

consider cd postive and b negative,a positive

so will get bc<ad

Not sufficient



st2-b<c<0


we have to consider case 3 and 4

case 3
consider a,b negative and c negative,d positive

bc>ad

case 4

consider c,d negative and b negative,a positive

bc>ad

sufficient.

My answer is B
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Re: is bc>ad? [#permalink] New post 10 Sep 2009, 23:15
Good question.
1)CD>AB;
In this case CD should pe positive and AB negative in order to satisfy the condition that ab/cd<0; So Eiher two numbers from CD should be positive or negative and one number from AB should be positive and another should be negative or vice versa. If we put different signs of numbers in equation bc>ad we will have different results, so insuff.
2) B<C<0
ab<0 and cd>0
so a - positive, and d - negative, let's put them into equation
bc>ad; on the left side we have positive number, on the right side we have negative number, Suff.
ab>0 and cd<0
so a - negative, and d - positive, and again
bc>ad; on the left side we have positive number, on the right side we have negative number, Suff.
So I choose B.
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Re: 7)if ab/cd <0, is bc>ad? st1 cd>ab st2 b<c<0 [#permalink] New post 30 Jan 2012, 13:39
Quote:
7)if ab/cd <0, is bc>ad?

st1 cd>ab

st2 b<c<0
7)if ab/cd <0, is bc>ad?

st1 cd>ab

st2 b<c<0


+1 B, good question

If \frac{ab}{cd} <0, ab > 0 and cd < 0, OR ab<0 and cd > 0.

Statement (1): cd > ab
So, cd > 0 and ab < 0
This could mean that c,d > 0 OR c,d<0
AND
a>0, b<0, OR a<0, b>0
If c,d >0 , a>0, and b<0, the result is bc<0 and ad>0, then answer is NO
If c,d <0 , a>0, and b<0, the result is bc>0 and ad<0, then answer is YES
INSUFF

Statement (2): b < c < 0, this means that bc >0
Then,
if a<0, d>0, so bc >0 AND ad<0, the answer is YES.
If a>0, d<0, so bc>0 AND ad<0, the answer is also YES.
SUFFICIENT

ANSWER : B

If someone has a faster method, that would be a great help!
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Re: 7)if ab/cd <0, is bc>ad? st1 cd>ab st2 b<c<0 [#permalink] New post 30 Jan 2012, 14:59
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If \frac{ab}{cd}<0, is bc>ad?

\frac{ab}{cd}<0 means that ab and cd have the opposite signs.

(1) cd > ab --> as they have the opposite signs then cd>0>ab --> c and d have the same sign, and a and b have the opposite signs. Now, if c, d and b are positive and a is negative then: bc>0>ad BUT if c, d and a are positive and b is negative then: bc<0<ad. Not sufficient.

(2) b < c < 0 --> bc>0 --> from \frac{b}{c}*\frac{a}{d}<0 as bc>0 then ad<0 --> bc>0>ad. Sufficient.

Answer: B.
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Re: If ab/cd < 0 , is bc > ad (1) cd > ab (2) b < c < 0 [#permalink] New post 02 Nov 2012, 15:37
what is the difficulty level of this question?
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Re: If ab/cd < 0 , is bc > ad (1) cd > ab (2) b < c < 0 [#permalink] New post 28 Mar 2014, 14:12
So we know that ac and cd have different signs. Now question is is bc>ad? Let's begin.

Staetment 1 cd>ab. Cd is positive and ab is negative. But still we don't know if bc>ad.

Statement 2 tells us that b and c are both negative hence bc is positivei. Now, what do we know about ad? Well, if ab/cd is negative and we already now that bc is positive then we have one negative more between a and d, anyways, ad will be negative and so bc>ad.

Therefore B stands

Hope this helps
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Re: If ab/cd < 0 , is bc > ad (1) cd > ab (2) b < c < 0 [#permalink] New post 04 Apr 2014, 23:25
yezz wrote:
If ab/cd < 0 , is bc > ad

(1) cd > ab

(2) b < c < 0


Sol:

either AB or CD is -ve & remaining one will be positive:

consider option 2 which is b<c<0 which means B and C are negative. negative*negative= positive. so combining the earlier given and this statement proves that ad should be negative.
i.e. either A or D is negative so -ve * +ve = -ve

+ve > -ve i.e. BC> AD
Hence B.
Re: If ab/cd < 0 , is bc > ad (1) cd > ab (2) b < c < 0   [#permalink] 04 Apr 2014, 23:25
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