Inequality DS

[rahul26]

Is n negative?

i)n5(1 - n4) < 0
ii) n4 - 1 < 0


(n5 refers to n to the power 5 and n4 above refers to n to the power 4)

[cramya]

I would go with C

Stmt I

n^5*(1-n^4) < 0

Either n^5<0 which would make n negative

or

1-n^4 < 0 n can be positive or negative

INSUFF

Stmt II

n^4 < 1

n=-1/2 n =1/2

INSUFF

Together

WE know n^4<1 so 1-n^4 is positive

Since n^5(1-n^4)<0 therefore n^5 neagtive and hence n is negative

Choose C

[rahul26]

Hi Cramya,
I agree with your ans i.e C.
But what if I approach the question as below:-
n^5(1-n^4) < 0
(n^5 - n^9) < 0
n^5 < n^9
Now if n is positive, n^5 < n^9 is always true.
Now if n is negative, n^5 > n^9 will always be true.

So is A not sufficient as one can deduce that n is always gretare then n.
I know I am missing some point somewhere.Please point out the same.

[codesnooker]

Now if n is positive, n^5 < n^9 is always true.

No the above statement will be always true only when n>1. If n lies between 0 and 1, i.e.

0 < n < 1, then

n^5 > n^9

Same case with your second statement.

Hence statement 1 is not alone sufficient.