my GRE questions

Okay brilliant people help me out here. I know these are all trick questions that I keep stumbling on my GRE prep test and I must master these!!!

1)

X²= 16 Y³= 64

A) X quantity is bigger

B) Y quantity is bigger

C) Two quantities are equal

D) Relationship cannot be determined from the information given.

Answer: D Fumiko's thoughts: X²= 16=4 x4 Y³= 64= 4x4x4 i.e. answer is C?

*shit, is it because X²= 16 --> X= + and - 4????

2)

The Average (arithmetic mean) of 12 and 20 is equal to the average (arithmetic mean) of 15 and X.

A) X quantity is bigger

B) 16 is bigger

C) Two quantities are equal

D) Relationship cannot be determined from the information given.

Answer: A Fumiko’s thoughts: (12+20)/2= (15+X)/2 solve for X. X=7 my answer is B.

3)

S is the set of all fractions of the form n/(n+1), where n is a positive integer less than 20.

A) Product of all the fractions that are in S.

B) 1/20 is bigger

C) Two quantities are equal

D) Relationship cannot be determined from the information given.

Answer:C fumiko’s thoughts: NONE. (didn’t want to take the time to solve it)