700 - 800 Inequality

[heshamelaziry]

Is a / b < 0 ?

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

(2) ab^4 < 0

[Talkativetree]

pretty sure C.

(1) tells us B is positive (odd exponent), but A could still be + or -
(2) tells us A is negative(exponent is odd), but B could still be + or -

together we know that a +/-<0

[heshamelaziry]

pretty sure C.

(1) tells us B is positive (odd exponent), but A could still be + or -
(2) tells us A is negative(exponent is odd), but B could still be + or -

together we know that a +/-<0

The way I understand this is:

Statement 1: a^2 is always +ve means that b^3 has to be +ve for the statement to be true

Statement 2: b^4 is always +ve means that a has to be -ve for the statement to be true.

I still can't deduce that one of the variables is +ve and the other is -ve ?

From your answer how can we say that b is +ve from b^3, if for example b= -1 and (-1)^3 is -1 ?

Thanks for patience

[tgf]

Because (taken together) from 2) you know that a<0 and for 1) to be positive b can't be negative (since a^2 is positive). So b>0.

Edit: Sorry the <, > signs should be replaced by +/- (sorry)

[Talkativetree]

we can deduce that B will always be + and A will always be - because the inequalities we are given in the two statements must be true. Also, what each statement gives us will never contradict the other statement, so we can make both assumptions

[mehravikas]

IMO - C

The answer has been already explained above, and my solution is exactly the same.

OA please?