Hi All,

We're told that Buckets X and Y contained only water and bucket Y was 1/2 full and that all of the water in bucket X was then poured into bucket Y. We're asked what fraction of the capacity of Y was then filled with water. This question can be approached in a couple of different ways, but it's worth noting that we do NOT know the relative sizes of the two buckets, nor do we know how 'full' Bucket X is to start. Until we have all of that information, there won't be any way to answer this question.

1) Before the water from X was poured, X was 1/3 full.

IF... the two buckets are the exact SAME size, then pouring the water from Bucket X into Bucket Y will make Bucket Y (1/2) + (1/3) = 5/6 full.
IF... the two buckets are the DIFFERENT sizes though, then the amount of water from Bucket X into Bucket Y would be different, so Bucket Y would be something OTHER than 5/6 full.
Fact 1 is INSUFFICIENT

2) X and Y have the SAME capacity.

This Fact tells us NOTHING about the amount of water in Bucket X, so there's no way to know how full Bucket Y would be after receiving the extra water from Bucket X.
Fact 2 is INSUFFICIENT

Combined, we know...
Before the water from X was poured, X was 1/3 full.
X and Y have the SAME capacity.

Since the two buckets are the exact SAME size, then pouring the water from Bucket X into Bucket Y will make Bucket Y (1/2) + (1/3) = 5/6 full.
Combined, SUFFICIENT

Final Answer: C

GMAT assassins aren't born, they're made,
Rich