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Is a/b < 0?

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Is a/b < 0? [#permalink]

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New post Updated on: 20 Jun 2011, 22:30
3
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A
B
C
D
E

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  25% (medium)

Question Stats:

70% (00:37) correct 30% (01:32) wrong based on 404 sessions

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Is a/b < 0?

(1) a^2/b^3 > 0

(2) ab^4 < 0

Originally posted by siddhans on 19 Jun 2011, 16:32.
Last edited by siddhans on 20 Jun 2011, 22:30, edited 1 time in total.
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Re: MGMAT DS [#permalink]

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New post 19 Jun 2011, 18:20
2
The answer is C.

(1) says that b > 0, since a^2 is always positive, so we don't know the sign of a. Insufficient.

(2) says a is negative as b^4 is always positive, so we don't know the sign of b. Insufficient.

(1) + (2) Sufficient as we know signs of both a and b.

Answer - C.
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Re: Positives and Negatives [#permalink]

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New post 10 May 2013, 21:21
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The question basically asks ....

IS \(lal\) < 0 ??

or a < 0 & a > 0 ......Does the value of a >0 & a <0 .....

Statement : 1 says ...... \(\sqrt{{a}} / l{b^3}l\) > 0

or \(\sqrt{{a}}\)> 0

or a > 0 ... Clearly Insufficient as it doesn't tell us if a< 0 also......Therefore, Insufficient.

Statement :: 2 ... Similar to statement it just tells us one part ... i.e;

as Given ... \(ab^4\) < 0 ... or a <0 .... Clearly, Insufficient.

1+2 ...... gives us that a<0 & a > 0 ..... Therefore, Sufficient.......

Hence, C ................. Hope it Helps !!
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Re: Is a/b < 0? (1)a^2/b^3 > 0 (2) ab^4 < 0 [#permalink]

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New post 08 Oct 2013, 08:35
Hi Bunuel/All ,

Why are we not considering a & b to be fractions?

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Re: Is a/b < 0? (1)a^2/b^3 > 0 (2) ab^4 < 0 [#permalink]

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New post 08 Oct 2013, 23:51
AkshayChittoria wrote:
Hi Bunuel/All ,

Why are we not considering a & b to be fractions?

Regards
Akshay


Responding to a pm:

a and b could be fractions. We are not assuming that they must be integers. We are only talking about their sign.

(1)a^2/b^3 > 0

It doesn't matter whether a and b are fractions or integers, a^2 will be positive. So b must be positive since positive/b^3 is positive. But we don't know whether a is positive or negative. Can't say about the sign of a/b

(2) ab^4 < 0

b^4 must be positive. So a must be negative because a/positive is negative. Can't say about the sign of a/b

Both together, b is positive and a is negative so a/b must be negative. Sufficient.
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Re: Is a/b < 0? [#permalink]

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New post 09 Oct 2013, 01:27
Thanks Karishma :) . I think sometimes it is better not to think too much and skip some possible scenarios :P :P .
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Re: Is a/b < 0? [#permalink]

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New post 17 Oct 2013, 02:26
Clumsy mistake.
I read st 2 as (ab)^4 <0
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Re: Is a/b < 0? [#permalink]

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New post 23 Sep 2016, 10:26
C is correct. Here's why:

(1) a^2/b^3 > 0

From this we know that b < 0, but we don't know whether a<0 or a>0, thus INSUFFICIENT

(2) ab^4 < 0

From this we know a < 0, but we don't know whether b>0 or b<0, thus INSUFFICIENT

(1) + (2) - We know a<0 and b>0, therefore we know a/b<0 SUFFICIENT
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Re: Is a/b < 0? [#permalink]

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New post 23 Feb 2017, 06:00
Prompt analysis
A and b are real numbers.
Superset
The answer will be either YES or NO.

Translation
In order to find the answer, we need:
1# exact value of a and b.
2# any equation to find the a and b
3# any equation to find the exact or the range for a/b

Statement analysis
St 1: a^2/b^3 >0. a^2 is always greater than zero. If the complete expression is positive, that means that b^3 is positive hence b is positive. But nothing can be said about a. INSUFFICIENT

St 2: ab^4<0. b^4 is always positive.nothing can be said about b though. To make the expression negative, a has to be negative.

St 1 & St 2: from st 1, we can say that b>0. From st 2, we can say that a<0. Therefore a/b <0.
Option C.
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Re: Is a/b < 0? [#permalink]

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New post 10 Aug 2017, 22:00
St1.
A can be + or -
B is +

St2.
A is -
B can be + or -

Together, A must be - and B must be +

C



siddhans wrote:
Is a/b < 0?

(1) a^2/b^3 > 0

(2) ab^4 < 0
Re: Is a/b < 0?   [#permalink] 10 Aug 2017, 22:00
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