Thank you for your quick reply...though, wouldn't 20% of X = 30% of Y mean that both clubs have the same number of members who are registered in both clubs? Maybe it will help me to grasp your reasonming if you could prove my reasoning in the first post invalid.

The Question reads as follows:
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.

The OG states that answer choice C shold be correct, however, this seems unreasonable to me. How can we get to any conclusion with the information given. It could be that Club X has 100 members in the first place and Club Y 200. Adding the % fractions wont change anything about the fact that Club Y will have more members than X. Saying Club X has 200 members and Club Y 100 resutls in the opposite solution.
Please .... help! What am I missing?

Let me first share my thought process:
Imagine this question as a set problem with clubs having X and Y members.
Now 1 statement says that the common members (lets say Z) are 20%X.
Assuming X= 100, 20% of X = 20. So Z=20.
Doesn't say anything about set Y . Hence Insufficient.

Now 2 says Z = 30%of Y . If Y is 100->Z=30.
Doesn't talk about X hence insufficient.

At this point answers A,B and D are out. Now combine A and B.
Consider A. If X=100 -> Z=20.
Now from 2. This 20 represent 30 % of the members in Y. Hence 30% of Y = 20.
There Y= 67(approx).

This will be the case every time.you can see that if you combine A and B with generic variables.
Z=20%X=30%Y.
X will always be Bigger. Hence C wins.

my process :
Total members = Members of X only (Say A) + Members of Y Only (Say B) + Members of Both
= A + B + both
Now from the statements both= either 0.2A or 0.3B
Total = A + B + 0.2A
or = A + B + 0.3B
Equating both
A + B + 0.2A= A + B +0.3B
0.2A=0.3B
A=1.5B
=> X>Y