Check out this image. Our task is to figure out which cup will fill up first, depending on how the liquid will flow through the pipes.
When we take a close look at the layout of the pipes connected to each cup, we can see that quite a few of the paths are clogged or blocked off.
The route leading to cup 1 is blocked. Same goes for cup 2. Cup 4’s path is also blocked. Cups 5, 6, and 7 are situated further down in the branching system, and their paths are either blocked or really long.
Cup 3 is the only one that has a clear, unobstructed path. So, it’ll be the first to fill up.