a data from gmat forum

[diebeatsthegmat]

Both a and b are positive; what is the value of a?

(1) 150 percent of a equals 450 percent of b.

(2) ab is the cube of a positive integer.
why is it not C
statement 1: 1,5a=4.5b or a=3 b
statement 2: ab= x^3 surely insufficient
1+2
ab=3b^2=x^3 so only b = 3 and since b =3 we can find a, right?

[Anurag@Gurome]

Both a and b are positive; what is the value of a?

(1) 150 percent of a equals 450 percent of b.

(2) ab is the cube of a positive integer.
why is it not C
statement 1: 1,5a=4.5b or a=3 b
statement 2: ab= x^3 surely insufficient
1+2
ab=3b^2=x^3 so only b = 3 and since b =3 we can find a, right?

(1) 150% of a = 450% of b
1.5a = 4.5b implies a = 3b; we don't know b, so cannot find a definite value of a; NOT sufficient.

(2) ab = x^3, where x is any positive integer; NOT sufficient.

Combining (1) and (2), 3b² = x^3
Now it is given that both a and b are positive, so they can be positive fractions or integers.
So, combining the statements also is NOT sufficient.

The correct answer is E.

[cans]

A) 150a = 450b or a=3b
insufficient
B) ab is cube. insufficient

A*B) ab = 3b^2 is cube. b=3 will do, also b = 24 will do... insufficient
IMO E

[diebeatsthegmat]

Both a and b are positive; what is the value of a?

(1) 150 percent of a equals 450 percent of b.

(2) ab is the cube of a positive integer.
why is it not C
statement 1: 1,5a=4.5b or a=3 b
statement 2: ab= x^3 surely insufficient
1+2
ab=3b^2=x^3 so only b = 3 and since b =3 we can find a, right?

(1) 150% of a = 450% of b
1.5a = 4.5b implies a = 3b; we don't know b, so cannot find a definite value of a; NOT sufficient.

(2) ab = x^3, where x is any positive integer; NOT sufficient.

Combining (1) and (2), 3b² = x^3
Now it is given that both a and b are positive, so they can be positive fractions or integers.
So, combining the statements also is NOT sufficient.

The correct answer is E.

oh yeah! i forgot "fraction" problem... thank you. you are so amazing!