Data Sufficiency

Elena89 wrote:Is the number of members of Club X greater than the number of members of Club Y ?

(1) Of the members of Club X, 20 percent are also
members of Club Y.
(2) Of the members of Club Y, 30 percent are also
members of Club X.

[spoiler]
How is the correct answer (C) ?[/spoiler]

Let the total number of members of Club X = X
and the total number of members of Club Y = Y
People who are members of both clubs X and Y = XY

(1) XY = 20% of X or XY = 0.2X
If X = 100, then XY = 20 but we do not anything about the members of club Y; NOT sufficient.

(2) XY = 30% of Y or XY = 0.3Y
If Y = 100, then XY = 30 but here but we do not anything about the members of club X; NOT sufficient.

Combining (1) and (2), XY = 0.2X = 0.3Y, which implies X = 3Y/2, so X is greater than Y; SUFFICIENT.

The correct answer is C.