Is a/b 0 (2) ab^4

Question

Is  \frac{a}{b} < 0 ?

(1)  \frac{a^2}{b^3} > 0

(2)  ab^4 < 0

KarishmaB · Accepted Answer

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.

subhashghosh · Answer

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.

manishuol · Answer

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 !!

AkshayChittoria · Answer

Hi Bunuel/All ,

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

Regards
Akshay

AkshayChittoria · Answer

Thanks Karishma

. I think sometimes it is better not to think too much and skip some possible scenarios

.

SaraLotfy · Answer

Clumsy mistake.
I read st 2 as (ab)^4 <0

law258 · Answer

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

KrishnakumarKA1 · Answer

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.

mrdlee23 · Answer

St1. 
A can be + or -
B is +

St2.
A is - 
B can be + or -

Together, A must be - and B must be +

C

Basshead · Answer

Is a/b < 0?

We can re-write the prompt as: Do a and b have  different  signs?

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

This statement tells us b is positive. No info about a. Insufficient.

(2) ab^4 < 0

This statement tells us that a is negative. No info about b. Insufficient.

(1&2) We can conclude b is positive and a is negative. Sufficient.

Answer is C.

bumpbot · Answer

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Is a/b < 0? (1) a^2/b^3 > 0 (2) ab^4 < 0

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