data sufficiency problem

[nidhis.1408]

IfA=2B,isA4 >B4?
(1) A2 = 4B2.
(2) 2A + B < A/2 + B.

[gmatblood]

It seems something is missing!

Whats the source of all these questions?

[nidhis.1408]

i am sorry. i just copy pasted d question and didnt realise that there "to the power" is wrong.

this is the correct question

If A = 2B, is A^4 > B^4?
(1) A^2 = 4B^2.
(2) 2A + B < A/2 + B.
(a) Statement (1) BY ITSELF is sufficient to answer the question, but statement (2) by itself is not.
(b) Statement (2) BY ITSELF is sufficient to answer the question, but statement (1) by itself is not.
(c) Statements (1) and (2) TAKEN TOGETHER are sufficient to answer the question, even though NEITHER statement BY ITSELF is sufficient.
(d) Either statement BY ITSELF is sufficient to answer the question.
(e) Statements (1) and (2) TAKEN TOGETHER are NOT sufficient to answer the question, requiring more data pertaining to the problem.



BTW source of the question is
https://www.hp-vietnam.com/GMAT-Practice-Test-1-Math.asp

[shankar.ashwin]

Given, A=2B , For finding A^4 > B^4? we need to know is A is +ve or -ve.

(1) A^2 = 4B^2. We cannot determine signs of A,B (Insuff)

(2) 2A + B < A/2 + B = 3/2 A < 0 (or) A<0.

We know A is -ve. B will also be -ve and a smaller number. Sufficient. B IMO

[user123321]

1) fails when A=0 and obeys above condition for rest of the values
hence not sufficient
2) after solving becomes A<0 => B<0
so always (2B)^4>B^4 because it eliminates the possibility of either of them becoming zero. hence sufficient.

user123321