I am reviewing a CAT and got this question wrong. I do not understand the explanation and the resulting answer (A). I *think* that what I don't understand and what the question may be hinging on is that given the question and 2 data points that we could find a numerical answer to this problem.

When doing the problem it was obvious to me that the problem translates to 2^3a(2^-2b) or 2^3a-2b. I think I mistakenly just said 3a-2b=0 and so 2b=3a b=(3/2)A.

So when I saw (1) I said to myself, 'no new info here, move along now sir' and saw (2) 2 and was like 'ok can plug in and get a value'

The explanation seems to posit that at some point the question becomes "what is 3a-2b" but I still don't understand why we wouldn't find a numerical value given that it's possible and have (C) as final answer. So, even if I mistakenly set 3a-2b=0 when it's just 3a-2b=? the first data point tells us that in fact 3a-2b does equal zero...but I don't see how that is the final answer when we are given the number 2 in (2) and could simply plug that in and get 3(2)-2(3)=ZERO. jghfdgjfdgjdfjgfd just typed out this entire response. going to post anyway and maybe it can serve as an example if anyone else was confounded by this answer. I still think the explanation given is not very clear.

You got b=3 from both statements.

1. b=1.5a

b=3/2*a
2b=3a
so 3a-2b=0

You only have to find whether you can find a value of the expression
with 1 you have 2^0 i.e. 1;

Option A says
Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Option C says
C BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

You can find the value of the expression with A alone, Option C says A is insufficient to solve the question.

Makes sense?

Yes, please let us know if you need additional help. :-)

_________________
Jamie Nelson
ManhattanGMAT Instructor