Puzzles are fun! Or they can be frustrating. Especially if you don't know the "trick" of the puzzle. When I tell you the answer for this one, you will be wise to every other puzzle of the same kind from here on out.
Hint: watch for blockages! You may THINK that liquid is flowing from glass to glass, but look carefully. Some glasses have no egress. The tube is not open, but closed, either at the top or at the bottom of the tube.
Therefore, in this particular puzzle ...
The liquid first flows into cup 1. About halfway up, it will start flowing into cup 3. Now, check the tubes "attached" to cup 3. The liquid has nowhere to go! Cup 3 is the answer!
You're welcome. ;-)
